Gene Van Buren, Kzoo Crew(Floor), Washington U. in St. Lou - #1 in Volleyball
------------------------------
Date: 7 Dec 92 23:54:33 GMT
From: Pat <prb@access.digex.com>
Subject: Terminal Velocity of DCX? (was Re: Shuttle ...)
Newsgroups: sci.space
In article <1992Dec7.173321.2812@ke4zv.uucp> gary@ke4zv.UUCP (Gary Coffman) writes:
>>
>>I think formula one race engines are good for about 1,000 miles.
>>they need to be able to do the Daytona 500;-).
>
>NASCAR stock cars do the Daytona 500, USAC Indy cars do Indy, Formula
>One races are much shorter, and twisty.
>
Oh.
>>But you see. you are proving my point. The DC will be a beefy
>>version of a spaceship. it will be the model-T of space, not a
>>Daimler Roadster. A truck compared to a racecar.
>
>That's what they said about Shuttle at a similar point in it's development.
>A space truck. As a *beefy* version of a spaceship, DC-X would qualify
>with a mass ratio of 2:1, but it's only intended to reach 30,000 feet,
>not orbit. DC-Y has a mass ratio of 100:1. That doesn't leave much
>room for "beefy".
>
Yeah, but with the shuttle, it was kinda bullshit from the start.
A truck does not have to be rebuilt everytime it returns to base.
Certainly, shuttle was a different approach from expendables, but it
really was a poor design approach. i think it was too ambitious
for technology, and starved for cash. i think had they spent some
more money up front and built the STS properly, we wouldn't have the problems
it has.
DC-Y may have a narrow mass margin, but i'll still consider it a success
if it makes a working ballistic shot. I am sure to pull of a decent
SSRT, yoou will need some better engines or higer performance
structural members or maybe even some solid boosters, but that
to me the real point of DC-Y is not to go to orbit and back with
cargo, but to even make it up there and back.
If you can show the approach to be right, from their it can be improved.
>>Gary, you have hit the point of the argument. It's religious.
>>You believe certain things about spacecraft, and not your mind
>>or your senses will alter it. People used to believe the same thing
>>about aircraft. Would you want to commute on a wright flyer?
>>how about on a COmet. People used to say Aircraft have to push the margins.
>>Well, somebody found away to increase the envelope.
>>Sure. early rockets were very marginal, but if you scale back your
>>expectations, you can increase reliability.
>
>Mass ratio is a very good measure of margin, and DC-Y's will be very
>very much pushing the envelope.
>
It's supposed to. it's a research plane. if it can consistently
get to a ballistic trajectory and demonstrate multiple re-entry
techniques, it will be a major advance.
>>>Look, I'm not trying to be dense here, but in circuit design we know
>>>that the more parts you have in a circuit, and the harder you push
>>>them, the more likely you'll have a failure. So you try to simplify,
>>>and beef up what remains to stand the maximum expected stress. Redundant
>>>power supplies tend to fail redundantly into a shorted load. Add protective
>>>circuits, and the protective circuits will fail in such a way as to take
>>>the system off line at the most critical moment. Simplicity, two wires
>>>make a light, the lever and the inclined plane, strict quality control,
>>>extensive testing, never depend on an active system when a passive system
>>>will do, never have two critical systems with a common failure point, always
>>>have a totally separate backup system, these are the routes to reliability
>>>in my business.
>>>
>>Exactly Gary. Your complaints are the shuttle. Your solutions are the DC.
>>The shuttle has 4 engine types, separate engines for each mode of flight,
>>three different heat protections, 8 cargo bay doors, .
>
>Yes, *totally* separate systems, completely different backup systems,
>*exactly* what I'm calling for above.
>
Yeah, but it's not redundancy. redundancy is the 747. 4 engines
with the ability to limp home on 2. would you consider a 747 to be
safer and more reliable if it had 8 engines. four props, four jets
where you run on jets at high altitude but exhaust all the fuel
and land and takeoff using props?
I instinctively like the DC concept of multiple engines all using
the same design. if you want to improve redundancy, put dual fuel pumps
and feeder lines to each engine just like on the LM.
Actually the LM is a great example. the Ascent engine only had
one nozzle and chamber, but it had serial parallel valves on
fuel feed.
The shuttle uses all these differient systems, each ahs to operate
within 5% of norm or you are screwed. look at launch.
3 SSME's, 2 SRBs must light, Exactly, precisely as planned.
if an SRB fails, write off the crew and vehicle. If an SSME fails,
You may have to do a RTLS abort at Hypersonic speed or have to jam
down in Gambia or spain.
Then you are getting to orbit. Youre SRBs are gone, the SSME's have
no fuel. You have two OMS engines to hit target orbit and make your
re-entry burn. If something fails, you end up using a lot of RCS
fuel up or scrubbing the mission.
THen finally, you make course adjustments and attitude control with
a final RCS system, using totally different fuels.
a DC can be more flexible and redundant with a single fuels system
and segregated tankage then the shuttle is.
If you have triple controllers, dual fuel lines. dual wiring to each controller, lots of isolation valves, i think you can make the system, very reliable
and redundant. and with less mass penalty then what the shuttle has.
>>DC,x,y,1 will have one common set of engines. the RCS i think uses
>>LH2/LOX. The same engines will do orbital manuevers, landing, takeoff.
>
>Single point failure. One system must do everything.
>
Make sure there are no single points. 8 engines are not a single failure
point. put dual controllers. put dual fuel lines. put serial/parallel
feed valves. put isolation valves. do what airliners fdo.
>>Gary. If the DC-X can pull off 100 flights in 1 year of testing, and no
>>major problems show up, will you stop complaining that it's unreliable?
>
>Absolutely. If anyone wants a craft with *no* payload capacity, a max
>altitude of 30,000 feet, and $10 million per flight, after 100 flights
>I'd concede that DC-X is just the ticket. Now if *DC-1* can deliver
>10 kilopounds to *orbit* 100 times in a year with no failures, I'd
>be much more impressed. I'd even consider buying a ticket. But there
>are many *giant* steps between DC-X and DC-1.
>
And i am sure everyone expects the DC-1 one to be many years off.
I guess you feel the X-15 was a useless waste of time. what kind of
spacecraft needs a mother ship, only hits 150,000 ft, wont beat Mach 7
and costs 200,000/flight. DC-X will prove the flight profile of the DC-Y,1
and hopefully demonstrate high reliability, fast turnaround...
