re: Chandra IPS-1 Burn Correction

Philip Chien (kc4yer@amsat.org)
Sat, 24 Jul 1999 20:04:12 -0400 

Ron Lee <ronlee@pcisys.net> said:

>>IPS-1  206/01:11:27  for 5min 00 sec
>
>Burn location is at about longitude 35 W, latitude 28.7 N.  European and
>African observers may see it. Uncertain if it will require optical aid
>but I would plan on it.

Actually it's at apogee (72030.56 km.) so it will be above the horizon in
most of Europe, all of Africa and South America, and much of Eastern North
America.  Basically if you're in darkness at 01:11 UT it will be above your
horizon and potentially visible.  Spacecraft will be illuminated at that
time.

For example, for myself at the Cape in Florida it's at Az 79 degrees, el 49
degrees -- but at Chandra's altitude the slant range is pretty long!

I'd give it a shot if you've got any decent optics.

What's interesting is plotting the ground track - it took me a couple of
seconds to realize that my tracking program was correct.  A satellite in a
24 hour elliptical orbit *does* result in a closed loop ground track.
(obviously for e= 0 it degenrates in to a typical plain geosynchronous
orbit)

Oh, and a reminder.  When Chandra reaches its operational orbit (and
probably even in most of the transfer orbits) it is extremely elliptical so
luni-solar pertubations are extremely important to model.  Many satellite
tracking programs do not take these factors in to account (and correctly so
since they're intended primarily for lower altitude more circular orbits)


And here's the info NASA's putting out about Chandra's orbit raising burns -

>The Chandra X-ray Observatory is moving toward the first firing of its
>Integral Propulsion System and all systems are performing well.
>
>Chandra's elliptical orbit continues with a perigee of 206 miles (329
>kilometers) and an apogee of 45,041 miles (72,065 kilometers).
>
> ... the first burn of Chandra's Integral
>Propulsion System. The firing of the engines is expected at about 9:11 p.m.
>EDT.
>
>Two of Chandra's four Liquid Apogee Engines will burn for approximately five
>minutes. There are two primary and two redundant engines. Each engine has
>105-pounds of thrust and use hydrazine as fuel with nitrogen tetroxide as
>the oxidizer.
>
>Tonight's burn will be the first of four apogee burns to increase Chandra's
>perigee.  There will be one perigee burn to increase the spacecraft's apogee
>during the mission. Burning at apogee is the best way to raise the orbit's
>perigee and vice versa. Burning at apogee and perigee is also the most
>efficient way to utilize fuel.
>
>Following the first Integral Propulsion System burn, the new perigee is
>expected to be 750 miles (1,200 kilometers) and the new apogee is expected
>to be 45,014 miles (72,023 kilometers). Chandra's new orbit duration will be
>24 hours, 38 minutes, slightly longer than its current orbit of 24 hours, 17
>minutes.
>
>At perigee, Chandra is traveling approximately 23,500 miles per hour (10.47
>kilometers per second).  After tonight's five-minute burn, the spacecraft
>velocity at perigee will be about 22,000 miles per hour (9.8 kilometers per
>second).



Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.