Re: Re doubts on the X-Prize
Hi everyone,
Yes indeed, there is a very big difference in the
propulsion requirements of sub-orbital and orbital
vehicles. In round figures it's 1 km/sec versus
8 km/sec - but the total energy required -
and the energy to be dissipated in re-entry -
is the square of the speed - so about 64 times
different.
Consequently the value of the XPrize is
controversial, with plenty of rocket engineers
saying it's too easy, and so of no engineering
value.
But I take the view - and I hope - that success
in sub-orbital space flights may break the "log-jam"
from which we've suffered for 30 years.
The problem is that the public BELIEVES that traveling
to orbit is very difficult and expensive and dangerous
because of unavoidable physical reasons. They don't
understand that the space agencies' having spent
$1 trillion over 40 years without having reduced
the cost of getting to space at all shows that they
haven't made any effort to do so.
And the Columbia accident has reinforced the public's
perception because they don't realise that it's a military
vehicle, not designed for low-cost passenger travel - of
no more relevance to passenger travel than a B-52 is to
tour operators' flights to Spain.
So when it becomes possible for anyone to go to space -
even for just a few minutes - for less than $100,000
- perceptions are likely to change greatly. Also, I
remain confident that the experience itself will be
so moving that it will become immensely popular.
After the development of scheduled sub-orbital flights,
it will then be just a matter of time before investors
invest in developing orbital services. Because by applying
some of the amazing technological progress that has
occurred since Gagarin, low-cost, safe orbital flight
is in fact also straightforward - though more difficult/
expensive than sub-orbital flights.
Of course, if an enlightened government somewhere in
the world (if there is one in relation to this matter) were
to invest a little appropriately they could accelerate the
whole process. But I guess that successful sub-orbital
flight services will educate the public irreversibly.
I hope so, anyway! :-)
Patrick
> 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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