Supersynchronous Transfer Orbit mission

[GeneCash]

I heard Proton is launching a comsat using a "supersynchronous transfer orbit" (SSTO) and I had never heard of such a thing, so I used a little Google-fu and found http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950021383_1995121383.pdf which is apparently the first time someone ever did this.

This is interesting, and it reads like a Scott Manley mission.

So they're launching this comsat on an Atlas IIA. Unfortunately, the normal ÃŽâ€V to GSO is over 1,750m/s, and would eat up all the satellite stationkeeping propellant doing the plane change. That would be bad.

Instead, they push apogee to 130,000km with the plane change there, plus they do 2 apogee burns and 2 perigee burns, which drops the ÃŽâ€V to 1,473m/s. That's nice, but it caused other problems:

* First, the transfer orbit was far longer than ever before (11-14 days) so they had to deal with battery life on the satellite so it'd live that long.

* Second, they had to get 2 Earth attitude sensor passes per orbit, except they couldn't use the sensor below 25,000km.

* Third, they'd never used the sensor over 100,000km before, and didn't know if it'd handle that small of an Earth disk or if it'd be accurate enough.

* They'd also never used the telemetry/command links that far out either. Plus, at various satellite attitudes, the antennae couldn't see the Earth at this altitude, so there was long outages, and they had to design the satellite so if things crapped out during an outage, it would survive to the next telemetry/command pass, AND there's only one ground station with the proper antenna to communicate with the satellite and all the burns have to be seen from that station to be commanded. (and you thought Remote-Tech was a b*tch!)

* Then, at this altitude, orbit determination is more difficult and you have to be a lot more precise. Those magic orbit numbers from MechJeb don't come for free!

* As if this isn't enough, they have to avoid certain launch times to avoid long battery-draining eclipses.

* They have to calculate Lunar effects since they're 1/3rd of the way to the Moon, and they have to avoid yet more launch times so the Moon doesn't drop the perigee into the ocean.

* The satellite has to end up in GSO at 322.5° East without hitting any other comsat on the way in.

WHEW. DAMN.

It's interesting that the launch got favorable winds which resulted in saving 45lbs of propellant, and they retargeted the launch orbit inclination in real-time from 26.9° to 25.7° to take advantage of it - and you thought Eve launches had to deal with razor-thin margins!

It's also interesting that they give the range/azimuth/elevation data graphs and explain how they did orbit determination. They found out that tracking SSTO wasn't that much harder than GTO.

They did have to upgrade their computer to do the trajectory firing solutions to a VAX 4000/90, and still had to make burn calculation runs of over an hour. They computed errors and margins down to 54 grams of propellant, and the final orbit had an eccentricity of 2.5x10e-4

Very impressive for 1994...

Edited December 9, 2013 by GeneCash

[KerBlammo!]

That's all rather gob-smacking, thanks for posting! Those real-time changes just seem like voodoo, to me.