As y'all probably know, DC-X is a low-speed flight regime testbed for a proposed reusable rocket-powered Single Stage To Orbit transport, McDonnell- Douglas Aerospace's (MDA) "Delta Clipper". DC-X is intended to prove out rocket-powered vertical takeoff, nose-first lifting-body to tail-first flight transition, and vertical landing. It is also intended to prove out both rapid turnaround of a reusable rocket by a minimal ground support crew, and rapid low-cost development of an advanced aerospace X-vehicle type engineering testbed by a small highly-motivated engineering team.
SDIO, the sponsoring organization, has brought DC-X to the verge of flight test in less than two years, for roughly $60 million, something a lot of established space outfits would have told you was impossible two years ago. The MDA team that built DC-X numbered a bit over a hundred people total.
DC-X stands roughly 40 feet tall on its landing legs, is 13 feet across the base, masses about 20,000 lbs empty and 40,000 lbs fully fuelled, and is powered by four 13,000 lb thrust Pratt & Whitney RL-10-a5 liquid oxygen/liquid hydrogen rocket motors. The RL-10-a5 is a special version the RL-10 designed for wide throttling range and sea-level operation.
The single DC-X vehicle was officially rolled out of its construction hangar at MDA's Huntington Beach CA plant at the start of April, then trucked out to White Sands, New Mexico for ground and then flight tests. Ground testing is underway, and flight testing should start in July.
As of Thursday, June 3rd, DC-X has undergone five ground test engine firings, with considerable progress being made toward readiness for flight. Chronology is as follows.
Engines shut down automatically after three seconds, before throttle ramp-up. Diagnosis was overly tight software limits; the system overall worked as designed. Vented hydrogen around the vehicle did ignite at one point and scorched off the SDIO and Delta Clipper logo decals. The vehicle was otherwise OK, having been designed for this. Anyone know a source for flameproof BMDO decals? The SDIO ones were going to have to go anyway.
Auto-shutdown before throttle-up again both times. Various minor problems identified and fixed, but the main trouble was again software that shut the engines down prior to throttle-up if all parameters weren't within tight tolerances. Main fix identified was to loosen tolerances in a sensible manner. The big news here was that the DC-X was fired, drained of fuel, worked on, fuelled, and fired again in an eight-hour span! This bodes well for meeting the nominal goal for a fast flight turnaround, three days.
First successful full planned duration engine firing run. Engines started at 30% throttle, ramped up to 65% after three seconds, then shut down after a bit over eight seconds, all as planned. Some cavitation in two of the LOX turbopumps, probably due to He gas being sucked in with the LOX. LOX loading procedures modified to prevent He bubbles near the LOX intakes.
Good firing, again to full planned duration, ten seconds, and throttle setting, 65%. LOX pump cavitation problem seen in previous test gone. A fire indication at a hydrogen vent turned out to be false, an artifact of readings due to extreme cold on the sensor. Such a fire would not have been a major problem in any case. An attempt to recycle the vehicle and do a 50 second engine run in the afternoon was scrubbed due to weather.
The next firing run should be early next week, Tuesday 6/8 or Wednesday 6/9. The interim will be taken up by the usual hardware testing and tweaking and some software modifications. This run may also include first firings of the gaseous O2/H2 reaction control system thrusters.
DC-X now has an engine-out landing capability added to the flight software. An engine conking out at takeoff will still likely destroy the vehicle, as there is insufficient thrust from three engines to keep DC-X in stable flight with full fuel (this is why an operational VTOL SSTO would have six to eight engines minimum) but if DC-X loses an engine before landing, new flight software mods should allow a controlled landing on three engines. The vehicle would likely take some damage from landing at an angle off the vertical, but repairable damage to DC-X should at worst delay the test program. Bending the vehicle at some point is practically a given in an experimental test flight program. As long as they don't break it, only one DC-X having been funded... <editorial note -- spare vehicles are cheap insurance in programs like this, typically costing only a small fraction of the overall program cost.>
First official DC-X flight (there will likely be short "stability test" hops done beforehand) still looks like happening in July. No way to pin it down closer than that, between New Mexico summer weather (thunderstorms) and the usual developmental uncertainties. Things look good, though.
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