From: aws@iti.org (Allen W. Sherzer)
Subject: Re: DC vs Shuttle capabilities
Organization: Evil Geniuses for a Better Tomorrow
Date: Mon, 14 Dec 1992 17:59:34 GMT

In article <g9g2v_p@rpi.edu> strider@clotho.acm.rpi.edu (Greg Moore) writes:

>	You missed my point.  If your crew compartment is in the cargo
>bay, where do you put the satellite?

First of all, which crew? The flight crew rides in the cockpit which is
above the cargo bay. If more crew are needed, then the satellite can
ride in the part of the cargo bay not used by the extra crew.

If it turns out that this isn't roomy enough, then you use the technology
developed under DC to build a larger vehicle. After all, DC will be a usefull
piece of technology but it isn't the only spaceship which will ever be built.

>	I eliminated some stuff above, but wanted to add some stuff here.
>Actually, plummeting launch costs may contribute to lower payload costs
>since people will be willing to build a less fault tolerant system
>knowing that if it fails, they can launch another cheaply.  

Exactly.

>As for on-site repair, for now DC-? fails for the same reason that
>the Shuttle normally does, it can't get up to GEO, you need a  OTV... 

Although a DC with a robot arm and some avionics changes may be the
OTV. Certainly the engines for a DC will be just what an OTV needs.

>>>	Also, as for retrieval, the Shuttle has shown that it ain't
>>>easy to do.  Will a two day on-orbit time be enough?

>>It may take modifications to the DC. At the very least you need to add
>>a robot arm and an airlock.

>	Granted, but that's not what I meant.  Will you have enough time
>to rendevous and capture the satelite?  It took what 3 days for the
>shuttle to capture Intelsat VI? That's aday more than DC-?.

Load the pallet with some extra power sources, add some solar cells and
your all set.

>Also, what type of fuel margin would DC-1 have for IN-orbit
>manevours? 

DC-Y has a fair amount of fuel for on orbit delta V but I don't
remember the exact numbers. How much DC has will depend on the
design requirements and who pays the bills.

But note that on a DC-Y you can power the fuel cells, main engines, and
RCS from the same source. This allows you some very powerful tradeoffs.

>(I realize it has enough for landing, and of course
>you don't wnt to cut into that for safety reasons.)

At least enough to get back to the orbital fuel dump.

>	Use it yes, but use it for what it can be used for economically.
>Let's see, we've added an airlock, an arm, additional on-orbit capacity.
>Hmm, that adds up, and add complexity.  Yes, let's ok at possibilities,
>but not claim t they are definites.

Agreed. But they don't look all that hard given a working DC.

>>My view is that we use the basic DC as a 'bus' which can be modified in
>>small ways to meet diverse missions. Costs are cut because the same assembly
>>lines are used to make DC1-EOT (Earth orbit transfer), DC1-OMV, and DC1-LM.

>	I have a question about this.  EOT and LM should require roughly
>the same amount of fuel, no? 

Pretty much.

>But how economical is it to transport that fuel TO orbit?  Am I correct in 
>remembering you saying about 10 DC-1 flights?

Yes it would take roughly 10 DC flights to carry up the fuel. Soon however
the availability of lunar oxygen and perhaps hydrogen will greatly reduce
that cost.

The bottom line however is that it is still a lot cheaper than the current
plans.

>	Also, does it make sense for the DC1-EOT and OMV and LM the same.

Not 100% the same. For an OMV I would strip off the thermal protection
system, add attach points outside for additional fuel and hardware (like
arms), I might look at lining it with solar cells for more power. For a LM
I think you would need to provide better insulation to reduce fuel boil off,
replace the landing gear to give it a larger footprint (like the Apollo LM),
and beef up the TPS for aerobreaking.

This will allow us to use the same core vehicle for multiple applications
which will allow development to be amortized over more vehicles and reduce
construction costs since we are building more core vehicles.

      Allen

-- 
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  aws@iti.org     |  nothing undone"                                       |
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