[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: A Few Questions

True enough .. I guess it just bugs me to think of taking a huge amount 
of delta-V and just throwing most of it away.  It probably is fairly 
economical to start with a GTO since that's the type of launch most 
people are doing already ..

My only remaining problem is that all aerobraking can do is lower 
apogee.  It can't raise anything because you're removing rather than 
adding energy.  Raising perigee requires an apogee kick, period, so 
getting to MEO would require propulsion.  Scrubbing a GTO down to a LEO 
just involves dipping into the upper atmosphere at perigee, and in order 
to avoid drag after that, you still have to get an apogee kick to raise 
the perigee above the atmosphere.  I'd imagine somebody just ran the 
numbers on that and realized aerobraking was essentially free delta-V 
and they could change orbits pretty easily with it.  That was probably 
the reasoning, and if someone else is already paying for the ride to 
GTO, it probably does make sense to hitch a ride on the booster.

No, hand launching wasn't that serious a suggestion.  ;-)  Even if the 
Russians *were* hand launching RS series birds from Mir.  Free floaters 
in LEO don't need to do any orbit changing.  I would be curious on what 
the numbers would be like for a GTO to MEO, with apogee and perigee 
burns, as opposed to a LEO to MEO with a Hohmann transfer ..

On Thursday, March 28, 2002, at 04:53 PM, Jeff Davis wrote:

> I am not familiar with their business model but they seem to be 
> targeting
> small payloads. With the advent of the Ariane 5 and a multi-small sat 
> launch
> platform I would guess that they believe it will be easier and more cost
> effective to be injected into GTO, then make an orbital manuever to a 
> lower
> orbit.
> Out of hand it may sound like a waste of energy but being a "for profit"
> corporation I'm assuming that they have done the math and figured that 
> there
> was either some cost saving, more frequent launch opportunity, or both 
> to
> have made such a business decision.
> I was only pointing out that reaching MEO doesn't necessarily require a 
> launch and then a bunch of fuel. It could be just as easily reached by 
> going
> to GTO and braking down to a lower orbit.
> Your point about about preferring an STS or Soyuz hand launch isn't 
> quite
> practical in the launch business since neither the Russians or NASA 
> would be
> too interested in taking a commercial (or amateur) bird, loaded with 
> fuel
> (the discussion about getting to MEO from LEO) along with them for a 
> ride.
> 73, Jeff-N9AVG
> ----- Original Message -----
> From: "Bruce Bostwick" <lihan161051@earthlink.net>
> To: <amsat-bb@AMSAT.Org>
> Sent: Thursday, March 28, 2002 4:50 PM
> Subject: Re: [amsat-bb] A Few Questions
>> How do they use aerobraking to raise the perigee?  You pretty much have
>> to burn at apogee to do that.  I suppose you could aerobrake to lower
>> apogee and turn a GTO into a LEO, but that's an enormous waste of 
>> energy
>> unless someone else is going out to GEO and dropping you off on the 
>> way,
>> a la AO-40/PAS-1R.  Also, once you lower the perigee enough to
>> aerobrake, you're probably not going to be able to raise it again
>> without having some sort of secondary propulsion system to give you
>> apogee kicks once you get to the right apogee altitude.
>> Personally, if I built a bird, I'd want to be well away from the GTO
>> trajectory, because there's a lot of discarded junk -- spent upper
>> stages, bits of thrust structure, SRB exhaust condensate, etc. -- on
>> that road and even a paint flake hitting a LEO bird at GTO perigee
>> velocity will kill it.  I'd feel much better with an actual LEO launch,
>> whether it meant an STS or Soyuz ride and a hand launch or some other
>> smaller booster ..
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
Heard from a flight instructor:
"The only dumb question is the one you DID NOT ask, resulting in my 
going out and having to identify your bits and pieces in the midst of 
torn and twisted metal."

Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org