Doubts on the X-Prize contenders
Dear friends,
this morning I got, from Stephen Ashwort (Space Age Associated), the message
hereafter referred, that -- for what I can understand (I am not a propulsion
expert) -- expresses doubts about the concrete chances of the X-Prize contenders
to really make the targeted job.
(also posted on http://www.tdf.it/cgi-bin/dcforum/DCForumID2/390.html )
: *** To all associates of Space Age ***
:
: Ross Sargent <rws.eighty@xxxxxxxxxxxxxx> has made the following comment.
: Anyone else out there like to present a view on the technical problems of
: suborbital versus orbital flight?
:
: Stephen
: 1 October 2003
:
: *****************************************************************************
:
: Stephen & Associates
:
: May I take this opportunity to say that I hope my pessimism regarding the
: future orbital capabilities of the X-Prize contenders is misplaced - this is
: one time I would love to be proved wrong. Your idea that orbital flight can
: be achieved in an incremental fashion seems, on the face of it, a reasonable
: suggestion. It is the numbers that cause the problem - this is just off the
: top of my head but I am looking for detailed information - a comparison of
: the speeds involved and, by implication, engine and thermal protection
: requirements is interesting.
:
: The projected Spaceship One reentry speed given at Scaled Composites page
: ( http://www.scaled.com/projects/tierone/New_Index/body.htm ) is 2500 mph.
: The reentry speed from Low Earth Orbit is 17500 mph or so - 7 times
: faster - requiring a far more capable heatshield with the added weight
: penalty this will incur. The mass margins for any spacecraft that is deemed
: even semi-reusable are very tight - obviously the more weight the bigger the
: engine required. Also in order to achieve orbital speed in the first place
: will require larger more efficient engines. In the case of Scaled they have
: opted for SpaceDev's hybrid motor and (you may be able to correct me here)
: Starchaser are still yet to decide on either bi-propellant or hybrid
: although both designs have been tested successfully. My concern is whether
: these motors will scale up to the requirements for orbital velocity or be
: suitable for large scale clustering. The burn time, combustion chamber
: pressure and regenerative cooling requirements are going to be far more
: rigorous for orbital access. Jim Benson, boss of SpaceDev, described his
: motor for Spaceship One as " almost directly suitable for the second stage
: of SpaceDev's Streaker launch vehicle. That booster would be capable of
: tossing 1,000 pounds (455 kilograms) of payload into low Earth orbit." Note
: that this is as a second stage motor lofting a mere 455 kilos! Whether there
: can be a smooth upgrade path to orbital flight, no matter how well funded by
: space tourist rides, is something I still have trouble seeing. Note that the
: X-Prize stipulates a 100 km (62.5 miles) altitude flying a similar
: trajectory to Alan Shepard's in a Mercury/Redstone combination - there is a
: good long way to go when one considers that the ISS orbits at approx 380/400
: km. (237/250 miles) - hence my slightly disparaging term "suborbital hop".
:
: I am an ardent proponent of manned spaceflight and find the prospect of
: actual launches by the various X-Prize teams thrilling, but there is a lot
: more engineering needed to cope with the altogether more demanding orbital
: requirements. As I said at the start I hope to be proved wrong - so whilst I
: look at some more figures in my role of reluctant devil's advocate will
: someone please comprehensively refute my pessimistic outlook?
:
: By the way I agree completely that those of us in the UK should support
: Starchaser's efforts - their chances of achieving any kind of crewed
: spaceflight are a darn' sight better than this government's - or any of
: their predecessors for that matter.
:
: best wishes
:
: Ross
:
: Ross W Sargent
: mailto:rws.eighty@xxxxxxxxxxxxxx
: The View from Number 80
: Skeptical Reviews
: http://www.eighty.btinternet.co.uk
: here is a Newsweek article on Rutan and the X-Prize, touting a possible
: flight on Dec 17th.
: http://www.msnbc.com/news/972359.asp?0dm=s12Bk
: *************** S P A C E A G E ***************
: http://www.astronist.demon.co.uk/saa00.html
: *************************************************
I thought it could be of some interest in this list, at least for the ones which
can give technical and/or economic opinions.
Aim high!
Adriano Autino
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-- Adriano Autino
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Technologies of the Frontier
web: www.tdf.it - e-mail: adriano.autino@xxxxxx
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