A kerosene-fueled X-33 as a single stage to orbit vehicle.
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From: Pat Flannery on 12 Apr 2010 02:25 On 4/11/2010 9:28 AM, hcobb wrote: > Since you need to reach Mach 25+ to orbit this saves you only 12% of > the speed requirement while imposing a requirement for an airframe > that can at least sustain that ground velocity while climbing. > > A much better result can be had from a balloon-assisted launch system > where the objective is to start the rocket with as much altitude as > possible rather than speed. > > http://academy.grc.nasa.gov/y2008/group-project/proposal-for-a-balloon-assisted-launch-system The problem with that is the size of the balloon needed to carry a large launch vehicle, which would make it very difficult to launch if there was any breeze. Balloon-assisted rocket launches have been done, but never into orbit: http://en.wikipedia.org/wiki/Rockoon Pat
From: Pat Flannery on 12 Apr 2010 03:14 On 4/11/2010 12:42 PM, hcobb wrote: >> Has *anyone* demonstrated that it is "better," student or otherwise? > > "however, no end product is currently capable of orbit insertion using > this method." Another problem is that if what it's suspended from is a unpowered balloon, you aren't going to be able to predict exactly where it will go in the high altitude winds. One of the competitors for the GUSTO program (that later became OXCART and developed the A-12/SR-71 Blackbird) was a Navy proposal for a inflatable rubber ramjet (I'm not making this up) that would be carried aloft by a huge balloon and then boosted by rockets to pick up speed till the ramjet reached ignition velocity. Kelly Johnson found this concept extremely amusing, especially when his BOTE calculations showed that the balloon to carry it would be around a mile in diameter. Pat
From: Peter Stickney on 12 Apr 2010 00:15 On Tue, 23 Mar 2010 09:23:07 -0800, Pat Flannery wrote: > That having been said, LH2 had once before led Lockheed astray: > http://en.wikipedia.org/wiki/Lockheed_CL-400_Suntan In retrospect, the > metallic tile concept for VentureStar may have been a flop if employed, > as they were supposed to be based on titanium, and as was discovered > after Columbia broke up on reentry, titanium burns at a lower > temperature than aluminum when in a atomic oxygen-rich environment; Sorry for picking this up late, but... Pat, the only person who is surprised that Titanium burns more easily than Aluminum is you. Anyone who has had to machine the stuff knows that it burns quite well. Titanium's advantage is that for moderately high temperatures, like cruising at Mach 3, it doesn't creep the way that Aluminum does. But it's no better at really high temps. Consider, if you will, that the Mach 6 X-15 was made of Iconel-X, which is pretty much Nickel. It's also why the structure of the Shuttle Orbiter is Aluminum. Since you need to keep the reentry heat out anyway - it's too high for Ti to handle, you're better off with an Aluminum structure. -- Pete Stickney Failure is not an option It comes bundled with the system
From: J. Clarke on 12 Apr 2010 00:52 On 4/12/2010 2:25 AM, Pat Flannery wrote: > On 4/11/2010 9:28 AM, hcobb wrote: > >> Since you need to reach Mach 25+ to orbit this saves you only 12% of >> the speed requirement while imposing a requirement for an airframe >> that can at least sustain that ground velocity while climbing. >> >> A much better result can be had from a balloon-assisted launch system >> where the objective is to start the rocket with as much altitude as >> possible rather than speed. >> >> http://academy.grc.nasa.gov/y2008/group-project/proposal-for-a-balloon-assisted-launch-system >> > > The problem with that is the size of the balloon needed to carry a large > launch vehicle, which would make it very difficult to launch if there > was any breeze. > Balloon-assisted rocket launches have been done, but never into orbit: > http://en.wikipedia.org/wiki/Rockoon The particular study was looking at launchers for satellites less than 10 kg and less than 1 kg in mass. Basically what Kruschev referred to as "grapefruitniks". But even on that scale the boosters are of the same magnitude in mass as the payload of the Hindenburg.
From: Pat Flannery on 12 Apr 2010 09:20
On 4/11/2010 8:15 PM, Peter Stickney wrote: > > Sorry for picking this up late, but... > Pat, the only person who is surprised that Titanium burns more easily than > Aluminum is you. > Anyone who has had to machine the stuff knows that it burns quite well. In powdered form it's used as an explosive in fireworks. > Titanium's advantage is that for moderately high temperatures, like cruising at > Mach 3, it doesn't creep the way that Aluminum does. But it's no better at really high > temps. Consider, if you will, that the Mach 6 X-15 was made of Iconel-X, which is > pretty much Nickel. It's also why the structure of the Shuttle Orbiter is Aluminum. > Since you need to keep the reentry heat out anyway - it's too high for Ti to handle, > you're better off with an Aluminum structure. The fact that it ignited at a lower temperature than aluminum alloy that was in its near vicinity in the presence of atomic oxygen came as quite a surprise for the Columbia Accident Investigation Board in their final report. They discovered that one of the windows (either the ones looking into the cargo bay or the ones just ahead of it on the orbiter's exterior) had to layers of metal vapor deposited on it, and the first layer was titanium, with aluminum deposited over that. This was determined to have come from the rollers at the upper center front end of the cargo bay where the doors closed together, which were made of both titanium and aluminum parts. The reason the Shuttle's internal structure was made of aluminum was that it was a lot easier to fabricate than titanium, and lower in cost as well. Since the TPS would keep the heat low enough internally to allow the use of aluminum alloys, that was the obvious way to go. Iconel-X would not have worked as a exterior material for the Shuttle either, as even it couldn't take the heat generated by reentry, and on the fastest flights of the X-15 they were reaching the limits of what it could do when they reached Mach 6, and sustaining airframe damage from the heat, especially if any sort of shockwave struck the aircraft's structure, like occurred on the flight with the dummy scramjet on the ventral fin that caused burn-throughs on the fin. VentureStar was supposed to slow rapidly enough during the early stages of reentry due to its low weight compared to its underbelly surface area once its propellants were used up that some sort of metallic tile TPS could be used. Lockheed never got specific about what those tiles were made of, but it was suggested that titanium was a major constituent in their structure. Pat |