Chandrayaan 3: Launch and Discussions

SriKumar · Post by **SriKumar** » 27 Aug 2023 20:51

juvva wrote: ↑27 Aug 2023 20:31
SriKumar wrote: ↑27 Aug 2023 19:44 Why would the temperature increase above the lunar surface relative to the surface. The heat on moon surface is entirely due to the solar radiation absorbed by the moon surface. I guess the above-the-surface measurements are being done not in shade, and are catching the sunlight directly (typical temperature measurements are done in shade on earth but on the moon it may be OK since there is no air or clouds to mess up the measurements).
since it is early in the morning ( at shiv shakti ) , the ground may be still retaining the cold of the night...

The temperature above the ground cannot be warmer than the temperature of the ground surface. (The only other source of energy to the thermometer would be direct sunlight, and typically temperatures readings are not taken in sunlight- but this may be an exception here and was a bit surprised to see it. The other possibility is that the thermometer above the ground is close to the rover itself which may be hotter than the ground from solar heating. Parts of the rover are black whereas all of the lunar soil is white, so one can expect the rover to absorb more solar energy. But this hypotesis assumes that the thermometer is in close proximity to the rover- which I dont know.).

On a different note, the Russian craft had a nuclear thermal source and now crashed on moon. I hope it buried itself properly but one cannot be sure.

Amber G. · Post by **Amber G.** » 27 Aug 2023 21:04

SriKumar wrote: ↑27 Aug 2023 19:44
SSSalvi wrote: ↑27 Aug 2023 16:45 Ye to kaam karna chalu kiya !!!
https://twitter.com/isro/status/1695725 ... 48/photo/1
Why would the temperature increase above the lunar surface relative to the surface. The heat on moon surface is entirely due to the solar radiation absorbed by the moon surface. I guess the above-the-surface measurements are being done not in shade, and are catching the sunlight directly (typical temperature measurements are done in shade on earth but on the moon it may be OK since there is no air or clouds to mess up the measurements).

FWIW: (Putting a physicist hat) Ignore if too much detail
- Temperature on moon (for any substance say rover or probe):
- Input
- (From solar radiation - calculate using heat-body radiation - energy mostly in visible spectrum ) (Major part of incoming energy)
- Reflected light from bright ground, far and near mountains, roaming rover -- again radiation
Very little conduction or convection as there is no air

-- Output - Head radiated (again radiation law depending on the temperature of the body)
Very little heat loss by air so can be neglected..

You reach an equilibrium. ( I can probably calculate/estimate the temperature fairly accurately if I can see a photo of the surrounding - I know position of Sun etc already -- and see the orientation/position/sunlight/shade etc..in the photo.. )
( Use E = σT^4 ... where E is the radiant heat emitted from a unit of area per unit time, T is the absolute temperature, and σ = 5.670367×10(−8) W. m−2⋅K−4 is the Stefan–Boltzmann constant ityadi... ityadi...)

sudarshan · Post by **sudarshan** » 27 Aug 2023 21:17

SriKumar wrote: ↑27 Aug 2023 20:51
The temperature above the ground cannot be warmer than the temperature of the ground surface. (The only other source of energy to the thermometer would be direct sunlight, and typically temperatures readings are not taken in sunlight- but this may be an exception here and was a bit surprised to see it. The other possibility is that the thermometer above the ground is close to the rover itself which may be hotter than the ground from solar heating. Parts of the rover are black whereas all of the lunar soil is white, so one can expect the rover to absorb more solar energy. But this hypotesis assumes that the thermometer is in close proximity to the rover- which I dont know.).

On a different note, the Russian craft had a nuclear thermal source and now crashed on moon. I hope it buried itself properly but one cannot be sure.

EDIT: WRONG INFO, PLEASE DISREGARD

Maybe you're reading the graph the wrong way? (Or I could be, I don't know). From what I could gather - the maximum depth that the probe could reach was 10 cm. So when they say "depth= -80 cm" that is actually 80 cm *above* the surface. In other words, a negative depth of 80 cm. Whereas +10 cm on the graph actually refers to 10 cm *below* the surface.

The clue is in the statement that the probe could reach a maximum depth of 10 cm only.

SriKumar · Post by **SriKumar** » 27 Aug 2023 21:27

I think you are right, sir.

It completely threw me off that a +ve value meant it was going deeper. So all but 3 of the measurements are actually above the ground (odd ). This squares with the linear drop in temperature as one goes above the ground and away from it.

The temp drops from 50 C to -10C in less than a meter above the surface!!

Corrected the correction. The -ve number is indeed depth below the surface. I too glossed over the units which are in mm and not cm.

amber.g- thanks for the notes and no, it is not too detailed for me. I used to solve such problems on Stefan's laws, Kirchoff laws and Newtons laws and Biot-Savart laws for breaksfast, lunch and dinner ages ago. Running calculations now has a bit more inertia to it but will try it at some point.

Amber G. · Post by **Amber G.** » 27 Aug 2023 21:35

On a different note, the Russian craft had a nuclear thermal source and now crashed on moon. I hope it buried itself properly but one cannot be sure.

Just to be clear - the Pu used there is not Pu239, but Pu238 -- Half life is about 87 years but it is all alpha particles, can't penetrate a tissue paper or your skin. (Primary danger is if it gets burned in atmosphere, and small particles gets inhaled).. You will get burned (it becomes really hot) if you touch it use oven mitts and you will be okay..no danger of radiation harm.

----

Maybe you're reading the graph the wrong way? (Or I could be, I don't know). From what I could gather - the maximum depth that the probe could reach was 10 cm. So when they say "depth= -80 cm" that is actually 80 cm *above* the surface. In other words, a negative depth of 80 cm. Whereas +10 cm on the graph actually refers to 10 cm *below* the surface.

The clue is in the statement that the probe could reach a maximum depth of 10 cm only.

May be I am missing the whole thing/context , or looking at wrong picture, but the picture I see, all depth measurements are in mm.... (not cm)..

sudarshan · Post by **sudarshan** » 27 Aug 2023 21:43

Amber G. wrote: ↑27 Aug 2023 21:35 May be missing the whole thing, or looking at wrong picture, but the picture I see, all depth measurements are in mm.... (not cm)..

Oh good lord

. Yes, that's mm, not cm. So then please disregard my previous blather, sorry. (I edited my earlier posts).

juvva · Post by **juvva** » 27 Aug 2023 21:55

assuming depth is measured in positive units ( more deeper greater the positive number ) , any explanation on why temperature increases with depth ?

Amber G. · Post by **Amber G.** » 27 Aug 2023 22:00

juvva wrote: ↑27 Aug 2023 21:55 assuming depth is measured in positive units ( more deeper greater the positive number ) , any explanation on why temperature increases with depth ?

^^^ See my post and picture posted above... Temperature does NOT increase with depth. At 8 cm below the surface, the temperature is -10 deg C. At close to surface it is 50 deg C of more.

Najunamar · Post by **Najunamar** » 27 Aug 2023 22:00

I have seen some hypotheses that the below surface temperatures tend to converge to tge average surface temp ata rate depending on the specific heat capacity of the regolith. But going below a certain depth would cause the temo to steadily increase as core is hotter...

Najunamar · Post by **Najunamar** » 27 Aug 2023 22:06

Would it be possible to use this lunathermal (?) power generation for future missions on moon? (huge temp variation using thermocouples generate power- could still work during lunar nights)...

SivaR · Post by **SivaR** » 27 Aug 2023 22:24

Kenya has many Geothermal power plants , but they use steam to generate electricity. But this kind of heat differential is really useful. Using heat pumps , this underground heat can be used to keep the habitat warm even during freezing temperature. This process is already in practice all over Europe. In-fact, European countries give subsidy to go for Heat Pump heating instead of Gas/Electric heating.

sanman · Post by **sanman** » 27 Aug 2023 23:20

Various interesting footage

Amber G. · Post by **Amber G.** » 28 Aug 2023 00:17

Amber G. wrote: ↑27 Aug 2023 20:15 Meanwhile:
Japan's lunar lander which will be launching tomorrow (28 August) at 5:56am (IST).

The lander named SLIM(Smart Lander for Investigating Moon) will demonstrate high precision pinpoint landing for future missions like LUPEX.

Just few hours wait..
SLIM also has a very efficient transfer trajectory to moon. It will be launched onboard a Mitsubishi H2A rocket as a rideshare along with the X-ray telescope XRISM.

(See figures below -- after first swing by to the moon, it will go much farther than moon's orbit and at the return perigee will be captured by the moon - Look the orbits carefully)...the paths are quite different than CY3) Longer path takes longer time but more fuel efficient...

SLIM will take few months to reach and then spend 1 month in lunar orbit before landing (~6 months total).
(will be happy to answer if there are questions about orbits )

SLIM is also carrying 2 LEVs(Lunar Excursion Vehicles). One is a hopper(LEV-1) and the other is a rover(LEV-2), both very compact and light weight.

Both will be ejected onto the surface when SLIM is few meters above the surface before touchdown.

LEV-1 is 2.1kg with dimensions of 26*40*30cm.

LEV-2 is manufactured by toy maker and is 250grams with a spherical shape of 80mm diameter.

Sources: https://www.isas.jaxa.jp/home/slim/SLIM/index.html
https://cosmos.isas.jaxa.jp/20-minutes- ... r-surface/

Good luck to them..
(Note that LUPEX (CY-4) is partnership between India and Japan.

Amber G. · Post by **Amber G.** » 28 Aug 2023 02:06

SriKumar wrote: ↑27 Aug 2023 21:27 amber.g- thanks for the notes and no, it is not too detailed for me. I used to solve such problems on Stefan's laws,

Thx...Just trying to help.. Stefan–(Boltzmann) law will do nicely.(and is straightforward)... once you know sun's temperature and distance from the sun.. (see sudarshan's post).. or you can take standard value of power in sunlight at moon and calculate at 70 lattitude .

(Or you can see the radiometer readings to find the average temperature at exact longitude/lattitude of the moon (see my post) and easily estimate temperature in shade or sunlight with lay of the land)

Need not worry so much about 'atmosphere'.. almost negligible compared to earth ...

Posting the temperature (average) at moon's surface) again..

.

Amber G. · Post by **Amber G.** » 28 Aug 2023 04:31

Like CY3, this launch is also on youtube..

Update: Lauch has been canceled due to weather..

sanman · Post by **sanman** » 28 Aug 2023 06:53

williams · Post by **williams** » 28 Aug 2023 08:52

Najunamar wrote: ↑27 Aug 2023 22:06 Would it be possible to use this lunathermal (?) power generation for future missions on moon? (huge temp variation using thermocouples generate power- could still work during lunar nights)...

Yes it is feasible to augment solar power and maybe more things can function with fewer sources of energy carried all the way to the moon.

Here is a simple experiment that demonstrates generating electricity out of temperature differences.

sanjaykumar · Post by **sanjaykumar** » 28 Aug 2023 09:31

What would an electricity generator design be that depends on the lunar day/night temperature gradient?

RCase · Post by **RCase** » 28 Aug 2023 10:39

Amber G. wrote: ↑27 Aug 2023 20:07 ^^^ (posting from above)ISRO:
Here are the first observations from the ChaSTE payload onboard Vikram Lander.

ChaSTE (Chandra's Surface Thermophysical Experiment) measures the temperature profile of the lunar topsoil around the pole, to understand the thermal behaviour of the moon's surface. It has a temperature probe equipped with a controlled penetration mechanism capable of reaching a depth of 10 cm beneath the surface. The probe is fitted with 10 individual temperature sensors.

The presented graph illustrates the temperature variations of the lunar surface/near-surface at various depths, as recorded during the probe's penetration. This is the first such profile for the lunar south pole. Detailed observations are underway

The temperature differential from the surface to 10 cm depth (which is not much, when you consider the hole you dig for planting a sapling in your backyard) is quite substantial. I would presume the core of the moon must have a high temperature, just like the earth's core temperature (probably not as high a temperature as the earth).

Q. Would the regolith be considered a good thermal conductor or a good thermal insulator?
If it is a good conductor, then thermal energy from the core must be seeping to the surface.
If it is a good insulator, the cooling down from the lunar night shouldn't cool the sub soil too much. My understanding is that the lunar day is extremely hot and lunar night is extremely cold and is constantly cycling every 14 days.

Using earth as an example, it takes a while for the ground to freeze in winters over a long period of winter.

SSSalvi · Post by **SSSalvi** » 28 Aug 2023 10:47

arvin wrote: ↑27 Aug 2023 17:59 ^^^
SSSalvi Sir, About RHU I dont think the news is credible.
If it indeed carried one, the CH3PM needs to have the distinctive radiator fins. None of it was visible.
DAE would have been involved from the very begining and safety measures would have different. Such things can't be done hush hush due to radiation concerns if launch fails.

True, Later searched for any other source for confirmation.. no one says so that there is any Atomic Radiative equipment.

Misguided by tweet from someone who had posted serious stuff earlier ( and even after the said post )

sanman · Post by **sanman** » 28 Aug 2023 11:56

RCase wrote: ↑28 Aug 2023 10:39 The temperature differential from the surface to 10 cm depth (which is not much, when you consider the hole you dig for planting a sapling in your backyard) is quite substantial. I would presume the core of the moon must have a high temperature, just like the earth's core temperature (probably not as high a temperature as the earth).

Q. Would the regolith be considered a good thermal conductor or a good thermal insulator?
If it is a good conductor, then thermal energy from the core must be seeping to the surface.
If it is a good insulator, the cooling down from the lunar night shouldn't cool the sub soil too much. My understanding is that the lunar day is extremely hot and lunar night is extremely cold and is constantly cycling every 14 days.

Using earth as an example, it takes a while for the ground to freeze in winters over a long period of winter.

If regolith was a good thermal conductor, then you wouldn't see such a large temperature gradient between surface and 10cm below surface.
So clearly it's a good insulator. This could be useful for piling it on top of habitation modules sitting on the lunar surface, in order to insulate and buffer against temperature swings from the day-night cycle. Additionally, piling it on top would further provide protection from micrometeoroid impacts, as well as solar & cosmic radiation.

SSSalvi · Post by **SSSalvi** » 28 Aug 2023 12:34

TOI science reporter Chethan Kumar Tweet: Reg his interview with CH3 project director P Veeramuthuvel.

https://twitter.com/chethan_dash/status ... 2164763887

Some tidbits. ( BOLD emphasis is mine )

Pragyan, has negotiated its first obstacle — a crater whose depth is approximately 100mm — boosting confidence of the team in control stations back on Earth. We were very anxious but that obstacle has been overcome.

rover operations are not fully autonomous and require commands to be sent from Earth.

Moving the rover from point A to B involves many steps. For every path planning, onboard navigation camera data must be downloaded to ground for generation of a digital elevation model (DEM)

…then ground & mechanisms teams will decide which path to take and uplink the command for the rover to follow,

The maximum DEM that can be generated is only for 5 metres each time the navigation camera sends images, which means every time the rover is commanded to move, it can at best cover 5 metres.

Isro has already done multiple rover movements as of Sunday.

…But there are limitations such as non-availability of telemetry and telecommunications 24/7, the need to track the sun continuously and so, the turnaround time between each movement operation is around five hours,

The Sun is not static there. Each day, there’s a 12° rotation, which needs to be accounted for

...the rover has deployable solar panel, where one side is fully mounted with solar cells but on the other side, only half the space is available,

Given that the rover is packed with telemetry, telecommand, battery, NGC, data handling storage, etc. power is crucial.

The data rate is also limited from the rover given that it can only communicate with the lander from where we need to download to ground.
This also consumes time as we need to also look at the science data coming in from the payloads…

Ashokk · Post by **Ashokk** » 28 Aug 2023 16:53

https://twitter.com/chandrayaan_3/statu ... 6241757664

Chandrayaan-3 Mission update:

On August 27, 2023, the Rover came across a 4-meter diameter crater positioned 3 meters ahead of its location. The Rover was commanded to retrace the path.

It's now safely heading on a new path.

vijayk · Post by **vijayk** » 28 Aug 2023 17:42

Great pictures

https://swarajyamag.com/science/chandra ... cle-course

SSSalvi · Post by **SSSalvi** » 28 Aug 2023 20:41

So near yet so Far.

Just at T-25 minutes, the Fully loaded and final countdown on, the Japanese Launch of SLIM/XRISM mission was aborted.
New date will be announced soon.

Amber G. · Post by **Amber G.** » 28 Aug 2023 21:18

SSSalvi wrote: ↑28 Aug 2023 10:47
arvin wrote: ↑27 Aug 2023 17:59 ^^^
SSSalvi Sir, About RHU I dont think the news is credible.
If it indeed carried one, the CH3PM needs to have the distinctive radiator fins. None of it was visible.
DAE would have been involved from the very begining and safety measures would have different. Such things can't be done hush hush due to radiation concerns if launch fails.
True, Later searched for any other source for confirmation.. no one says so that there is any Atomic Radiative equipment.

Misguided by tweet from someone who had posted serious stuff earlier ( and even after the said post )

I saw that tweet too, and agree with you. To be fair, the tweet, mentioned that it was speculative/not confirmed.. I did not take it seriously.
Having said that, it is not really a big deal.. or that sensational ( for newspapers/ aamjanta 'nuclear' /atomic is taken much more seriously than it ought too.)

Few comments:

RHU (Radioisotope heater unit) is not RTG (Radioisotope thermoelectric generator) - RHU is a small device, it provides heat through radioactive decay and normally provide about one watt of heat (derived from the decay of less than 2 gms of Pu-238 (Po 210 weight even less). Total mass, including shielding is typically about 40 gms. It produces heat for several decades. USA has used Pu238 (Half life ~88 years). Russia in previous lunar missions used Po210 (Half life few months). (For moon mission like CY3 Po 210 can be used)

I don't know about India ( ISRO have asked for proposals to develop units).

Producing Pu-238 is much more complex (technically challenging) than Pu-239 etc.. Pu-239 is much easier to produce if you have a reactor..

)

In US, DoE has general-purpose heat source (GPHS) primarily for space use. These units have several pellets of Pu-238 all cladded in iridium - size about 5 cm x 10 cm (weighing about a Kg) for component heating.

RHU does not have thermo-couples etc.. it does not produces electric power - just keeps electronics warm.
(RTG converts only a tiny percentage of energy into electricity - rest of the heat is dispersed in space - hence fins etc.. it gets very hot. Pu-238 pellets can be handled (with gloves or may be oven mittens) - no risk of radiation etc..

Amber G. · Post by **Amber G.** » 28 Aug 2023 21:19

SSSalvi wrote: ↑28 Aug 2023 20:41 So near yet so Far.

Just at T-25 minutes, the Fully loaded and final countdown on, the Japanese Launch of SLIM/XRISM mission was aborted.
New date will be announced soon.

Sad.. Due to bad weather -- Was watching live (see my post above the you tube link video is still there)..

Good news in the days of fast computers and better understanding of planets gravitational fields, they don't have to wait for months or years for the next launch window... (For perspective, in Apollo 11 case, if the launch window would have been missed the next window would not have arrived for several months/year -- they would have used Apollo 12's window... These orbit calculations are pretty complex .. used to take months of computer time in 60's)

One thing fascinates me - see the orbit/path .. (I posted here )... see how SLIM goes around moon for the first time - slingshots to 2-3 times far away from the moon and catches it back near the perigee ... slow and study --- 4-5 months to reach the target and travels a long distance but saves the fuel..

Amber G. · Post by **Amber G.** » 28 Aug 2023 23:57

Near precision landing - Difference between the Actual & Targeted landing site is ~358m..
(SLIM's is ambitiously planning within 100 m .. for future landings)

Amber G. · Post by **Amber G.** » 29 Aug 2023 01:54

@sudarsan @srikumar @rcase and others - interested in temperatures, regolith etc - serious interest in these items:

Allow me to give a good background:

CY3 is doing the measurements on the ground but lot of things we know quite well from remote sensing..

- Diviner Lunar Radiometer Experiment has measured (Billions of readings in last many years - since 2009) and mapped the whole lunar surface in details there is a data base (huge) for temperature readings for the whole Lunar surface.
(ISRO and others have access to it)... very detail every location, 15 minutes interval over a long time...

- One map I posted before, for example, and other maps, reveal the complex and extreme nature of the lunar surface thermal environment.

- Also detail models on how the regolith stores and exchanges thermal energy with space.
- Daytime maximum temperatures are sensitive to the radiative properties of the surface.
- Nighttime temperatures are sensitive to the thermophysical properties of the regolith.

>>> Daytime maximum temperatures are sensitive to the albedo of the surface and are ∼387–397 K at the equator, dropping to ∼95 K just before sunrise, though anomalously warm areas characterized by high rock abundances can be > 50 K warmer than the zonal average nighttime temperatures. An asymmetry is observed between the morning and afternoon temperatures due to the thermal inertia of the lunar regolith with the dusk terminator ∼30 K warmer than the dawn terminator at the equator. An increase in albedo with incidence angle is required to explain the observed decrease in temperatures with latitude. At incidence angles exceeding ∼40°, topography and surface roughness influence temperatures resulting in increasing scatter in temperatures and anisothermality between Diviner channels.

Nighttime temperatures are sensitive to the thermophysical properties of the regolith. High thermal inertia (TI) materials such as large rocks, remain warmer during the long lunar night and result in anomalously warm nighttime temperatures and anisothermality in the Diviner channels. Anomalous maximum and minimum temperatures are highlighted by subtracting the zonal mean temperatures from maps. Terrains can be characterized as low or high reflectance and low or high TI. Low maximum temperatures result from high reflectance surfaces while low minimum temperatures from low-TI material. Conversely, high maximum temperatures result from dark surface, and high minimum temperatures from high-TI materials.

Impact craters are found to modify regolith properties over large distances. The thermal signature of Tycho is asymmetric, consistent with an oblique impact coming from the west. Some prominent crater rays are visible in the thermal data and require material with a higher thermal inertial than nominal regolith. The influence of the formation of the Orientale basin on the regolith properties is observable over a substantial portion of the western hemisphere despite its age (∼3.8 Gyr), and may have contributed to mixing of highland and mare material on the southwest margin of Oceanus Procellarum where the gradient in radiative properties at the mare-highland contact is broad (∼200 km). <<<<

CY3 will give direct measurements to deduce thermo properties of the regolith.

sanman · Post by **sanman** » 29 Aug 2023 02:07

Amber G. wrote: ↑28 Aug 2023 21:19 Good news in the days of fast computers and better understanding of planets gravitational fields, they don't have to wait for months or years for the next launch window... (For perspective, in Apollo 11 case, if the launch window would have been missed the next window would not have arrived for several months/year -- they would have used Apollo 12's window... These orbit calculations are pretty complex .. used to take months of computer time in 60's)

One thing fascinates me - see the orbit/path .. (I posted here )... see how SLIM goes around moon for the first time - slingshots to 2-3 times far away from the moon and catches it back near the perigee ... slow and study --- 4-5 months to reach the target and travels a long distance but saves the fuel..

So I wonder how much more they're paying for the additional operations time, just to save on some small amount of fuel.
I thought Japan has plenty of lift capacity to spare with its H-2A and now even H-3 rockets.
Japan doesn't optimize for costs, it seems. Their rockets are very mass-efficient, with the highest amount of composites. But they're expensive as well.

I look forward to India's next Moon mission, which will be done as a collaboration with Japan. India is only providing the land, while Japan is providing the launch vehicle and the rover that will roll around on the Moon. That mission is being called LUPEX (Lunar Polar Exploration), and will also look for lunar water.

Since BARC is developing Radioisotope Thermal Generators (RTG), I'm hoping that a future Indian lunar mission will feature these. to help Indian rovers & landers survive the cold lunar night. Will also be useful for missions to outer solar system.

And since launching any nuclear payload is always controversial, I wonder if our in-flight abort tests for Gaganyaan would prove useful in developing safety measures for payloads containing nuclear materials?

Amber G. · Post by **Amber G.** » 29 Aug 2023 03:13

sanman wrote: ↑29 Aug 2023 02:07
Since BARC is developing Radioisotope Thermal Generators (RTG), I'm hoping that a future Indian lunar mission will feature these. to help Indian rovers & landers survive the cold lunar night. Will also be useful for missions to outer solar system.

And since launching any nuclear payload is always controversial, I wonder if our in-flight abort tests for Gaganyaan would prove useful in developing safety measures for payloads containing nuclear materials?

I do not have any reliable information about status of "BARC's developing RTG" . I know they have asked for some proposals ...(I could make some educated guesses but that could be inaccurate -- and even if it might not be, it will be highly irresponsible to discuss in an open forum).. Let somebody with credible - official information give details.

What I can say is Producing Pu-238 is a complex and resource-intensive process. It requires specialized facilities, nuclear reactors, and significant expertise in handling radioactive materials. Production of Pu-238 is expensive due to the technical challenges among other things. US is one of the few countries with the capability to produce Pu-238 for space missions. DOE is responsible for producing Pu-238 for NASA's space exploration programs.

Check out Wiki https://en.wikipedia.org/wiki/Radioisot ... _generator for more information and status of other countries using them..

(RHU is much easier to get as it is much smaller ityadi.. needs only about 2gm of Pu238)

The production of Pu-238 involves specialized facilities and expertise, making it a capability that only a limited number of countries possess. Other countries with advanced nuclear programs obviously have technical capability to produce Pu-238, but it's not publicly known (at least to me

to what extent or whether they actively engage in its production. (My information is from top of my head - recently things may have changed in last few years. )

Polonium-210 (Po-210).. which might be good for CY3 type mission - is a highly radioactive isotope ,,. Po-210 is an alpha emitter and can provide a compact and efficient source of heat for power generation but ..Po-210 has significant radiation hazards .. Its production and use are subject to strict regulations etc....

Anyway, FWIW: He Here's a simplified overview of the production process .. (:) )

Neptunium-237 (Np-237) is irradiated in a nuclear reactor with neutrons. Np-237 captures a neutron, undergoes beta decay, and transforms into Pu-238.The resulting Pu-238 is chemically separated from the remaining irradiated material. The separated Pu-238 is then further processed and purified.
(Check out any good text book

)

Amber G. · Post by **Amber G.** » 29 Aug 2023 04:06

sanman wrote: ↑29 Aug 2023 02:07
So I wonder how much more they're paying for the additional operations time, just to save on some small amount of fuel.

Make no mistake it is BIG, VERY BIG deal..it is not just "small amount of fuel" .. it is about the ability of sending a space probe of desired payload (mass) to a destination which would not be possible otherwise -- even with a much bigger rocket.!!

For perspective, let me just give a small example: All probes to outer planets like Pioneer, Voyager 1, Voyager 2 etc had very complicated trajectories... many even went to Venus (for gravity assist), took help from Jupiter on their way to Saturn etc...

Voyager 2 used Venus for gravity assists. TWICE!! It conducted two separate Venus gravity assists in 1979 to set up its trajectory for encounters with Jupiter and Saturn!

And timing was such, the planners, requested to hurry up and passing of the budget and approval of the plan , because if they missed the window, next such alignment will not happen at least for the next 10 years!

That was with SATURN rockets -- very powerful ones. (Even the most powerful rockets on the earth would not be sufficient for such a mission without such a long/ calculated planned trajectories if one is sending even a small payload to outer planets.

For Moon mission, if we are lucky to get more powerful rockets, we can cut the elapse time... we can also increase pay load significantly by using smart fuel efficient trajectories. Spending extra few months may not be that important...

This is why many of us are very impressed with ISRO's magic in planning the trajectory . and near perfect execution ....no small feet. (Same with SLIM's trajectory -- would be intersting to see the execution)

Atmavik · Post by **Atmavik** » 29 Aug 2023 04:27

https://youtu.be/WVrWcbyOmxY?si=DReyCxIoE4x3AGaM

This video explains some other routes that can be taken to the Moon.

A Naive question - how did Soyuz get to the moon using a direct route when its lift capacity is smaller than LVM3 ? Was its payload lighter ? What am I missing ? Maybe comparing lift capacity is too simplistic ?

sanman · Post by **sanman** » 29 Aug 2023 04:27

Interview with Chandrayaan-3 Project Director P Veeramuthuvel with insights on rover operations:

https://timesofindia.indiatimes.com/ind ... 111021.cms

Progress of the scientific experiments is good, expecting good results.
Rover operations aren't fully autonomous, requires full involvement of the ground teams.
Telemetry and telecommunications are not available 24/7; Rover-to-Lander data rate is low
Rover movements account for changes in Sun elevation which shifts by 12° each day.
Due to these, turnaround time between each movement operation is around five hours.
Navcam based DEM generation is limited to 5 meters. So rover path planning and movement is limited by that.

Amber G. · Post by **Amber G.** » 29 Aug 2023 04:45

Atmavik wrote: ↑29 Aug 2023 04:27

A Naive question - how did Soyuz get to the moon using a direct route when its lift capacity is smaller than LVM3 ? Was its payload lighter ? What am I missing ? Maybe comparing lift capacity is too simplistic ?

Perhaps I am missing something but..
Soyuz spacecraft has not been used for direct missions to the Moon. The Soyuz spacecraft is primarily used by Russia for crewed missions to the International Space Station (ISS) and other orbital missions.

LVM3 has been used for various missions, including launching satellites into orbit.

The Soviet Union, during the period of its Luna program, used a variety of rockets for their Moon missions. The most notable were the Proton and N1 rockets.

The Proton rocket was a heavy-lift launch vehicle developed in the Soviet Union. While it wasn't used for direct crewed Moon missions, it played a significant role in launching robotic missions to the Moon, like the Luna landers and orbiters.

The Proton rocket had multiple variants, and it was known for its powerful capability to lift heavy payloads into orbit. The most powerful variants of the Proton rocket, like the Proton-K, could carry payloads of around 20-23 metric tons to low Earth orbit (LEO).

The N1 rocket was the Soviet Union's ambitious attempt to send cosmonauts to the Moon as part of the Soviet manned lunar program. However, the N1 rocket faced numerous technical challenges and failed in all launch attempts.

Comparing to GSLV Mk III (LVM3):
The GSLV Mk III (LVM3) is a heavy-lift launch vehicle designed to carry large payloads into both geostationary and low Earth orbits.
Not expert on payload but capacity of is about 4-5 tons to geostationary transfer orbit (GTO)

In terms of payload capacity, the GSLV Mk III (LVM3) is significantly smaller than the powerful variants of the Proton.

sanman · Post by **sanman** » 29 Aug 2023 05:06

Amber G. wrote: ↑29 Aug 2023 04:06 Make no mistake it is BIG, VERY BIG deal..it is not just "small amount of fuel" .. it is about the ability of sending a space probe of desired payload (mass) to a destination which would not be possible otherwise -- even with a much bigger rocket.!!

WIkipedia says the mass of the Japanese spacecraft is 590kg. https://en.wikipedia.org/wiki/Smart_Lan ... ating_Moon
Meanwhile Chandrayaan-3 had total weight of 3900kg.

SLIM's overall development cost is estimated at roughly 15 billion yen ($102 million). So pretty cheap by Japanese standards.

For perspective, let me just give a small example: All probes to outer planets like Pioneer, Voyager 1, Voyager 2 etc had very complicated trajectories... many even went to Venus (for gravity assist), took help from Jupiter on their way to Saturn etc...

Voyager 2 used Venus for gravity assists. TWICE!! It conducted two separate Venus gravity assists in 1979 to set up its trajectory for encounters with Jupiter and Saturn!

And timing was such, the planners, requested to hurry up and passing of the budget and approval of the plan , because if they missed the window, next such alignment will not happen at least for the next 10 years!

That was with SATURN rockets -- very powerful ones. (Even the most powerful rockets on the earth would not be sufficient for such a mission without such a long/ calculated planned trajectories if one is sending even a small payload to outer planets.

For this reason, I'm a fan of NASA's Deep Space 1 mission, which used xenon ion-thruster propulsion, which greatly reduced the propellant mass.
The NASA people said Deep Space 1 with its ion propulsion handled "like a dream".

For Moon mission, if we are lucky to get more powerful rockets, we can cut the elapse time... we can also increase pay load significantly by using smart fuel efficient trajectories. Spending extra few months may not be that important...

This is why many of us are very impressed with ISRO's magic in planning the trajectory . and near perfect execution ....no small feet. (Same with SLIM's trajectory -- would be intersting to see the execution)

ESA's Smart-1 mission also flew to the Moon using ion thrust propulsion. I wonder if ISRO might see benefit in using ion thrust to get to the Moon?

vnms · Post by **vnms** » 29 Aug 2023 05:50

For manned missions to deep space, ion engines will not do.

The planned nuclear thermal propulsion engines will reduce the time to, say, mars from 6 months to around 45 days.

Constant thrust engines, although having ng a lower ISP, will be able to provide a greater delta v over a period of time. A far great velocity can be achieved with a fraction of the fuel required by the traditional rocket engines new.

vnms · Post by **vnms** » 29 Aug 2023 05:56

ISRO and other organizations must now focus on nuclear powered engines as this is the future andif we want to go beyond the moon.

Building bigger rockets simply will not do as they are way too expensive and the development time is not practical.

We need to focus on reusable launchers and nuclear power based engines.

I think ISRO has proved, beyond all doubts, it's capabilities with regards to trajectories and timing (Mangalyaan and CYx)

Amber G. · Post by **Amber G.** » 29 Aug 2023 07:06

Atmavik wrote: ↑29 Aug 2023 04:27 https://youtu.be/WVrWcbyOmxY?si=DReyCxIoE4x3AGaM

This video explains some other routes that can be taken to the Moon.

Thank you, for putting this video!!!
Got a chance to watch the video, I studied orbital mechanics way back as a graduate student - in late 1960's in IIT-K and have taught these type of courses... to physicists, engineers and students with different backgrounds but I could not have done it better to explain without ton of mathematics ... this is as good as it gets, very difficult subject, explained it nicely and accurately mathematics wise. Highly recommend for those who really want to understand math/science behind this..

This is still an open field of research ... and there can still be complex orbits which are more efficient -- to be discovered.

And yes, The ion propulsion system on DS1 performed exceptionally well.

Thanks again.

And yes, Smart -1 worked nicely too..

Added later -

I wonder if ISRO might see benefit in using ion thrust to get to the Moon?

May be someone else will give more details (or I may post some later in other dhaga ..) but ...

Yes, ISRO has been actively working on ion propulsion technology for its space missions ..

Eg Chandrayaan-1, included an experiment called the "Charged Particle Monitor" (CHACE). CHACE was designed to measure the exosphere of the Moon and the solar wind interaction with the lunar surface. While not e ion propulsion system, it demonstrated ISRO's interest in ionized particle measurements..

The GSAT-20 communication satellite .. features an ion propulsion system for orbit raising and station-keeping maneuvers.

(I am not that tuned to ISRO's current status and developments in space technology is changing rapidly in ISRO )

Atmavik · Post by **Atmavik** » 29 Aug 2023 07:33

Amber G. wrote: ↑29 Aug 2023 04:45
Perhaps I am missing something but..
Soyuz spacecraft has not been used for direct missions to the Moon. The Soyuz spacecraft is primarily used by Russia for crewed missions to the International Space Station (ISS) and other orbital missions.

the Russian Luna 25 was launched on Soyuz 2b(a beautiful rocket) this has a Max GTO capacity of 3200 odd kgs. the payload was only 30 kg compared to chandrayans 2000 + kg . i think thats why i could go t the moon much faster. i should have googled this but was on phone..