Re: Direct Launch Proposal

T C MCKEAN wrote:
"Rand Simberg" <simberg.interglobal@xxxxxxxxx> wrote in message news:45ac7283.523515114@xxxxxxxxxxxxxxxxxxxx

On 28 Oct 2006 07:53:38 -0700, in a place far, far away, "Space Cadet"
<kaw211@xxxxxxxxx> made the phosphor on my monitor glow in such a way
as to indicate that:


Hey all have you seen this?

http://www.directlauncher.com/

"DIRECT is an alternative approach to launching missions planned under
NASA's new mandate: The Vision for Space Exploration (VSE). DIRECT
would replace the separate Ares-I Crew Launch Vehicle (CLV) and Ares-V
Cargo Launch Vehicle (CaLV) with one single "Universal Launcher",
capable of performing both roles.

This architecture completely removes the costs & risks associated with
developing and operating a second launcher system, saving NASA $19
Billion in development costs, and a further $16 Billion in operational
costs over the next 20 years.

What do you think of this?

Yawn...

Why do they just find a way to enhance a horizontal lift craft which takes off like a normal plane? I find these verticle lift off vehicles appear to be more problems and inheretly dangerous than a posible horizontal lift off vehicle would be.
I am totally clueless in airodynamics and the physics of breaking through the atmospheric boundary and know it takes quite a bit of calculations to do so, but a horizontal take off vehicle should be able to manuveur into the right trajectory to break the boundary. It seems to me the shuttle type launch as it now exists does nothing to further the commercial use of attaining an orbit or allowing possible futher entry into a non orbital trajectory such as the moon or beond.
Is the current rocket approach the only possible feasable way of getting into orbit?
Tina


No, but...

First, 'horizontal lift' can mean many things. The only HTHL that could take off from a runway, ascend to orbit, de-orbit and return to the same or other runway is one that does signifigant airbreathing along the way. I don't have high hopes for those, with the possible exception of Skylon (or similar) craft that don't try air-breathing into double-digit Mach numbers, and go all-rocket getting out of atmospheric drag and heating, before going hypersonic.

But either way, the landing gear must be able to support the gross loft-off weight of the ship (GLOW), and above a certain point, that particular structure starts eating into payload.

You can get around it by launching with a rocket sled with attachment hardpoints dorectly to the ship's frame, but you've now given up normal runway takeoff (you can only launch where the rocket sled setup exists, and only in directions the sled tracks point), and an early abort means dumping lots of fuel before your landing gear can handle the weight. (not that jettisoning fuel prior to an emergency landing is something new) and returning, probably gliding, to a runway. (more on that later)

Or, you can have something that launches vertically, but lands horizontally (the shuttle, for instance, but your design could be an SSTO like that intended for the VentureStar with no ETs or SRBs to get rid of first) Bt that means there's a 'dead man zone' between launch commit, and getting high and fast enough to get horizontal, if you have to abort during ascent (the shuttle has no real options before SRB burnout and jettison, and an RTLS doesn't look like fun, either...you really want to at least be able to do a Trans-Atlantic Abort [TAL] if you can.) Anything earlier, and you're likely screwed. Expect to lose at *least* the vehicle.

Vertical take off and landing vehicles (VTVL or VTOL) don'thave to re-orient themselves in an abort during ascent, and can recover from situations that a VTHL could not (the DC-X unintentionally demonstrated this, when gaseous hydrogen that unexpectly got into its aeroshell and ignited, explosively destroying part of said aeroshell, carried out an emergency landing by throttling back and descending again. Something similar on X-33 might well have led to a smoking hole in the ground, as it could not have acheived gliding flight at that point, and would have had poor gliding characteristics, if it did). Though again, a fuel jettison would be both desirable (for safety reasons) and necessary (for landing gear support reasons...an orbit-capable VTVL likely would, as the DC-X did, sit on strongpoints on its frame at launch, not the landing gear.

After a normal return form space, we get back to the old argument:

A winged vehicle (espically as most deigns are glders at this point) must be certain of reaching a runway of sufficent length, and has only one pass at it.

A vertical lander counts on air-start of its rocket engines, with not much more fuel on board than necessary to power the terminal deceleration and landing of a now very light vehicle...but it can put down on any open, reasonably hard an flat spot, if necessary.

A winged vehicle has to carry the weight of those wings to space and back (only airbreathers would make much use of them, on the way up.).

A vertical lander has to carry that amount of fuel saved for landing, to space and back.

Expendables, by definition, don't care about landing, but they throw away hardware every time.

However, my impression is (and anyone with better numbers is welcome to comment), once you start talking orbital payloads over, perhaps 20,000 pounds, and *definitely* as you approach or exceed 100,000 pounds, VTLV systems win out. The landing gear issue now dominates for horizontal launchers, while, like the DC-X did, a vertical launcher can sit directly on strongpoints on its frame when on the pad, using light landing gear (retracted at launch and needing no wheels) to support a then-much lighter ship (even with signifigant return payload) when returning.

Take your choice.

Those (and, I'm sure, a bunch of other things I didn't mention, didn't think of, or just don't know) are the decisions you have to make in the design process....but don't dismiss VTVL because it's not as familiar as wings. (Indeed to some, they land in a much more satisfying, classic spaceship manner, often described as '...the way God and Robert Heinlein intended') and they may be your *only* choice, if you and/or the market needs a re-useable launcher that can take heavy payloads to orbit in one shot.

(And if orbital refueling's available, VTVLs make acceptable, though not optimal vehicles capable of going on to the Moon and back. [with aerobraking on return] A winged vehicle would be clumsier, if not impossible in that role.)

And I'm sure someone will mention space elevators, and that's certainly another possibility, but I believe it's *much* farther term than the above.

--

Frank

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