Satellite Payloads: Discussion/News

[Guest]

This thread will discuss desirable and "do-able" (hint, hint )
satellite payloads w.r.t. the challenges, costs/benefits etc.
I will start out with a brief note on two payloads.

SBAS (Satellite based augmentation systems.)
SBAS typically uses
a geostationary satellite to beam down error-correction signals that increase
the accuracy and availability of GPS/GLONASS signals. The economic benefits
can be huge because SBAS/GPS can be used as a alternative to
(expensive and per-airport) instrument-aided landing systems that help pilots land aircraft in poor visibility conditions.

(See graphic on accuracy improvement with WAAS... USA's SBAS.))

[Rudra]

juicy thread. lots of meat to chew on. the
first figure -shouldn't GPS accuracy increase with
SBAS on. it says the opposite.

btw lot of chip verification work for Thuraya
was done in hughes sw systems in gurgaon. the
chip(s) were made by Ericsson I think.

infact most japanese make printers, copiers,
fax machines etc have indic sw in it. they seem
to prefer outsourcing it to blore.

So would I be right in saying that the handheld
GPS kits used by IAF pilots are accurate to 100ms
only. Is there any open-src work that says we
use GLONASS in our a/c ? Does russia allow us
to decrypt the mil-std GLONASS signals ?

[Guest]

Originally posted by Rudra Singha:
the first figure -shouldn't GPS accuracy increase with SBAS on. it says the opposite.

Hi Rudra, The SA on/off in the first figure refers to "Selective Avalability" and not SBAS. SA was the system where the US government deliberately degraded the civilian band signal to reduce accuracy. SA was turned off (increasing accuracy) on the night between May 1st and 2nd, 2000. This was critical in increasing commercial/civilian demand for GPS systems because it enabled street-navigation/fleet-maintenance which was impossible with the poor accuracy caused by selective availability. See the image below to see how the error was reduced by the removal of SA.

<img src="http://www.igeb.gov/sa/timeline.gif" alt="" />

WAAS is USA's SBAS system and it increases accuracy compared to the base (SA off) GPS signal.

Originally posted by Rudra Singha:

So would I be right in saying that the handheld
GPS kits used by IAF pilots are accurate to 100ms
only. Is there any open-src work that says we
use GLONASS in our a/c ? Does russia allow us
to decrypt the mil-std GLONASS signals ?

100mts accuracy was in the SA days. Today (with SA off), if they're using standard GPS receivers, the error should be under 15mts (95% of the time). I am not aware of GLONASS signal usage... but one presentation by ISRO people mentions both GPS and GLONASS... so I included it in there. If I find the reference I'll post it here.

P.S. To answer your question on another thread, I'm not from the Northeast. I am originally from Bangalore, currently in USA.

[Rudra]

15 mts should be good enough for a 1000lb'er
against exposed type targets. this will give us
a desi-JDAM and hence ability to strike fixed
targets in any kind of cloud cover or night without the time-on-station and danger of LGB designation.

LGBs/TGBs can then be used for targets requiring more accuracy or mobile targets whose locations are just discovered on the fly.

I think its high time IAF moved to super-hardened heavy bunker buster bombs of 1000lb and up using
the metallurgy developed in various DRDO labs for
tank ammunition.

1000lb - jags, M2ks, su30mkis
2000lb - jags (centerline pylon?),su30mkis
5000lb - can MKI carry this behemoth? certain deeply buried targets like PAF C3I stations might need this one. it has to have thick tungsten
casing and be long and thin to reduce drag and
concentrate the momentum.

I have this "vision" of 15 mkis roaring over
a 'pindi ISI HQ and delivering about 30 2000lber's
on the dot.

[Guest]

"ISRO to develop micro-satellites."
http://www.hinduonnet.com/thehindu/holnus/08131601.htm

Dorky report...it says "The day was not too far when satellites could be put together under a microscope."

ISRO is preparing PSLV for a cluster mode of
launching micro-satellites. A Circular Spacecraft
Deck was being developed to aid in configuring the
spacecraft launch to any specific need. It could
carry four mini-satellites up to 300 kg or six micro-satellites, according to ISRO sources.

I am not sure what's new about this. KITSAT (107 kg), TUBSAT (45 kg), PROBA (94 kg), BIRD (92 kg) were all micro satellites anyway.

[Umrao]

<I> "Dorky report...it says "The day was not too far when satellites could be put together under a microscope." </I>