Suborbital Spaceflight Update

HobbySpacer writes "Burt Rutan's group has fixed a problem with the SpaceShipOne and recently carried out a successful drop test. Ground studies involved tests with CFD - "creative Ford driving" using a Ford-250 pickup truck. Other suborbital news includes the announcement of plans to follow the X PRIZE competition with an annual X PRIZE Cup event in which rocket teams will compete in an air show type format. In Japan the RVT (Reusable Vehicle Test) just completed its third short hop (in Japanese) within a week. (English reports on the first and second flights.) The liquid hydrogen/liquid oxygen powered vehicle seeks to develop robust, reusable technologies for vertical takeoff and landing rockets. It and subsequent vehicles will gradually expand the flight envelope to high altitudes."

Comments

Suborbital

[powerlord]

Okay, This just occured to me but, they haven't tested the engines yet, and the X-Prise is supposed to place them into sub-orbital. How close are they going to be to have to deal with re-entry? (ie. could one of the teams accidentally "over-achieve"?)

While I doubt this will happen, I'm just wondering what sort of margin for error exists.

Re:Suborbital

[fredmosby]

Some of the flights of the X-15 had problems with bouncing off of the atmosphere, and the flight plan for space ship one is almost exactly the same. So they probably do have to worry about re-entry to some extent.

Re:Suborbital

[henley]

OOOh, I'm going to blow karma on a pedantry trip

Technically speaking, the only way to "Bounce off" the atmosphere is if you're coming in at greater than earth's escape velocity. If you're travelling slower than escape velocity, the best you can manage is a "loft" that trades height for speed. The golden rule here is: Once your non-interplanetary vehicle encounters the sensible atmosphere, your time in orbit is just about over.

The only vehicles for which "Bounce" was a serious problem were the Apollo capsules and Russia's Zond lunar spacecraft (which never flew manned). In the case of Apollo, "Skipping" was a serious consideration since although the trajectories ensured that even at lunar-reentry speeds, the atmosphere would be re-encountered, this could take 2-3 days on a looonggg orbit - a problem when the Command Module held power, fuel and other consumables for only 2-3 hours independent flight (having ditched the Service Module at this point). The re-entry programs and manual reversion procedures thus focussed on ensuring that a skip absolutely did not happen, at the expense of a hard ride down and loss of targetting, if necessary.

In the case of the X-15, however, the problems were different although related. Because the X-15 only got up to about Mach 6 (remembering that even low-earth orbit requires a speed of Mach 25), there was never any question of performing a significant "Bounce". Nevertheless, the conditions on an X-15 re-entry were severe enough that a Thermal Protection System (TPS) was required. Problem was, this was designed for the X-15's original target speed of Mach 5 and used a "heat-sink" inconel structure to absorb the heat whilst retaining strength. This worked just about OK, however when the X-15-A2 mods were made (external fuel tanks to increase deltaV hence re-entry speeds), this increase was enough to overload the TPS. The solution attempted was to spray a coating of (pink) ablative material over the X-15 before each flight, and let it burn off during re-entry. This proved problematic, not least of all because the charring ablative coated the pilot's windscreen! A more serious problem was caused by an experiment attached to the lower ventral fin, a mock-up of a hypersonic ramjet. At the increased speeds encountered by the X-15-A2, the shock waves from this ramjet impinged on the lower fin (rather than streaming past) and caused sufficient local heating to "eat" away the fin's structure.

Whilst it may be tempting to assign all of these problems to the "should have known better" category, remember that A) The X-15 was designed in the '50s. Using slide-rules and paper, and best judgement rather than fancy-dancy CFD codes and CAD/CAM. B) The X is important: it means that it's a vehicle designed to find out what the issues and problems are with a particular flight regime, and to test potential solutions.

SpaceShipOne's flight program is similar to the X-15 in many respects, but is lower-energy (Mach3 vs Mach5-7). They can expect to see greatly reduced heat load problems during their re-entry profile because of this, as well as having a novel way of dealing with it in a controlled fashion.

who tends to fund these projects?

[rizzn]

I've been a consultant for an aircraft project for about eight years, and one of the problems we've run into over and over again is funding. Whenever an aerospace idea tries to break the mold or move from traditionally taught ideas, it seems it's generally shunned by the aerospace community. Looking at the pictures shown on their site, they are some fairly fanciful designs -- ones that certainly wouldn't be looked at from the aerospace circles we run in. So who exactly funds these projects, private investors, companies?

Re:CFD, for the curious

[Thagg]

Burt Rutan has used truck-mounted systems for years to do the equivalent of wind-tunnel tests. It makes a tremendous amount of sense, mostly because it is super cheap.

To build a wind tunnel to test a full-scale airplane would cost tens of millions of dollars. The tunnels at Nasa Ames in Mountain View have been shut down because it's too expensive to run them -- to run the fans in the 120x80 tunnel took more than 100 megawatts.

On the other hand, driving a truck down the runway will generate the same windspeeds over the airplane using about 100 horsepower or about 75 kilowatts, more than 1000 times as efficient.

Burt's early van-based systems for testing the VariEze used very cute aerodynamic balances to measure the forces on the airplane models. In pictures I've seen he had a model on one side of a pivot, and a circular disk on the other side. The circular disk generates a known amount of drag, and by moving it closer and further from the pivot will show how much drag/lift/whatever the model was generating.

Disclaimer -- I tried but failed to name my son Elbert.

thad

I've seen this before somewhere

[CaptainCarrot]

Is it just me, or does that Japanese vehicle look a lot like the McDonnell-Douglas DC-X they were experimenting with a few years ago?

I work for a competitor, but I've always regretted the DC-X getting its funding cut. It looked like it was a truly innovative idea and had a lot of promise.

Re:How would NASA handle this problem

[Anonymous Coward]

Rutan is gonna win this thing on December 17th.

If you knew anything about the industry, you'd know that Rutan
doesn't know his aerospace from his arse.

NASCAR = IAMRAD

[Baldrson]

How about all those young studs who want to risk turning themselves into hamburger for speed and glory leaving NASCAR and going to form the International Association for Manned Rocket Aeronautical Dragsters; or IAMRAD.

Rather than a 1/4 mile horizontal drag race, make it ia 1 mile vertical drag race with total flight staying within the limits of Class E airspace, preferably below 14,500 ft.

Start with the Rocket Guy's 15,000 ft flight as a standard and do exhibitions involving dual launches of these vehicles. Grandstands must of course be at a safe distance but you don't need to be too close to something like this for the thrill of your life. There's a lot more energy being released in these drags than a typical 1/4 mile drag of course, and a lot higher likelihood of fatalities to the "drivers" but if you move it out to a remote area you can have some serious fun while developing the flight systems needed to carry men to orbit.

I like the X-Prize and all but really there needs to be some serious motor-head madness here with the motor babes and all.

A side benefit of this sort of competition is we get to find out if the spam in a can idea of manned rocketry is actually superior to human guidance. We all know someone will just have to attempt human guided rockets.