Chair Force Engineer

Monday, April 25, 2011

The New Mercury-Atlas

When I saw this story on, my eyes were immediately drawn to the graphic of the Boeing CST-100 space capsule on top of the Atlas V rocket. While previous artwork from United Launch Alliance showed a generic capsule on top of the Atlas, this is the first illustration of the complete CST-100 + Atlas V 401 stack. Apparently this is an unmanned cargo configuration due to the missing Launch Escape Tower (unless Boeing has some ideas similar to SpaceX for crew escape.)

There's no elegant way to mount a capsule to the skinny Atlas V rocket and its even-skinnier Centaur upper stage (as long as the Centaur isn't wearing its 5-meter fairing for large payloads.) So Boeing went with a short and wide tapered section between the CST-100 service module and the Centaur upper stage. By eyeballing the picture, it appears that the CST-100's diameter is around 4 meters--pretty close to the 3.8 meter diameter of the Atlas V. This would put the CST-100 in a similar size-class as the Apollo spacecraft. It should be able to carry three astronauts in comfort on long missions, or 5-6 for emergency rescue missions from the ISS.

I was reflecting on the early orbital spaceflights which used the Mercury spacecraft and Atlas booster. Since Boeing owns the manufacturer of Mercury (McDonnell Aircraft) and wants to use the Atlas booster, why not just rename the CST the Mercury? If nothing else, enthusiasts for manned spaceflight can be very nostalgic.

Tuesday, April 19, 2011

An End to Escape Towers?

Since the earliest days of human-rated space capsules, it's always been a challenge to safely tear the capsule away from a launcher that was exploding or boosting off-course. The system devised by the great NASA engineer Max Faget was a tower equipped with a powerful solid rocket that would attach to the front of the capsule. Escape towers debuted during Project Mercury and were reused for the Apollo & Soyuz spacecraft (still used today by the latter!)

During the pad & early launch phase, the escape tower is a heavy but effective method to pull a capsule and crew to safety. The engines on the capsule's service module or the other rocket stages lack the thrust or the response time to act in situations where the capsule needs to accelerate from a standstill to escape its booster, or where it needs to boost downrange and reorient itself into an attitude where the heat shield bears the brunt of the aerodynamic heating before the capsule can deploy its parachutes and land.

After the early portion of ascent (usually around or shortly after stage II ignition,) an escape tower is no longer needed. The service module or upper stages can get the capsule safely downrange, or even all the way to orbit. The abort mode is determined by the phase of the launch where the failure occurs. During Soyuz 18a, the bad separation of stage 2 & 3 led to an abort using the service module engine. Soyuz T-10 used the escape tower after the rocket caught fire on the launch pad prior to launch. One space shuttle mission even aborted to orbit after a main engine shut down early.

Engineers have recognized the limitations of launch escape towers, particularly how they are quite heavy for a piece of equipment that is only useful for less than two minutes during ascent. Gemini capsules got around this using ejection seats, but only because the aerozine-nitrogen tetroxide fireball of an exploding Titan rocket would be more contained than the boosters of Mercury. Former NASA administrator mike Griffin promoted his Max Launch Abort System, a shroud which housed four solid rockets and fit over the capsule. Now SpaceX will demonstrate a new launch escape system under a $75 million contract with NASA. The escape rockets would be completely contained within the Dragon capsule. It could very well work, but it does bring two concerns to mind. For starters, the mass of the escape rockets would make it all the way to orbit. And the use of multiple escape rockets reduces the system's reliability when compared with the single-rocket designs of the past. But it will be interesting to see if SpaceX can come up with an effective solution to this old problem.

Monday, April 18, 2011

Polar Express

One of the most surprising aspects about the recent Falcon heavy announcement was SpaceX's decision to make Vandenberg Air Force Base the initial launch site for their new heavy-lift rocket. The selection of Vandenberg indicates that Falcon Heavy will be launching to the south and south-southwest, putting payloads into retrograde and highly-inclined orbits like the ever-useful sun-synchronous orbit.

Highly-inclined orbits have many advantages, particularly for sensor missions. They can observe a large fraction of the earth's surface due to the wide range of latitudes they travel. Sun-synchronous orbits provide constant coverage by passing over the same point on the earth's surface at the same time every day.

Most satellites that have been launched into highly-inclined orbits have been military in nature. So it stands to reason that the Pentagon may have some uses in mind for the Falcon Heavy. In the past, the Pentagon has expressed little interest in rockets bigger than the Titan IV (which replaced the shuttle's military mission) or Delta IV Heavy. The only proposed payload requiring a bigger rocket was the Zenith Star space laser.

I have always viewed Falcon Heavy as a launcher to support manned spaceflight, able to lift components and propellant for space stations, or for spacecraft designed for flight beyond earth's orbit. Yet those payloads are best assembled in low-inclination orbits and launched to the east from Cape Canaveral. This puts the spacecraft in an inclination that will not requiring the burning of too much propellant as it departs on a plane connecting the earth with the intended destination (moon, Mars, asteroid or other celestial body.)

Thus far, no human has ever launched into a near-polar orbit. Originally the space shuttle was supposed to fly some missions from the "cursed" SLC-6 launch pad at Vandenberg, a plan that was cancelled after Challenger was lost. The Vandenberg missions necessitated the shuttle's big wings, so the orbiter would have enough range to glide cross-track back to its California landing site after one orbit. (After all, the earth processes roughly 45 degrees after one orbit period for a shuttle in low earth orbit.) Because the Van Allen radiation belts emanate from an axis passing near the earth's poles, the astronauts would be exposed to a much higher radiation dose than on missions with lower inclinations. For winged spacecraft like the shuttle, the near-polar trajectories greatly limit launch aborts similar to the Trans-Atlantic Abort for easterly launches, which would allow a shuttle to land downrange (no luck landing a shuttle in Antarctica!) This is less of a problem for capsule-type spacecraft, which can set down anywhere in the ocean as long as a recovery ship is within a reasonable distance.

So what does this mean for Falcon Heavy's potential payloads? At this point it's more of a mystery than the Falcon Heavy upper stage or the first-stage crossfeed system (which will be the subject of an upcoming post.)

Saturday, April 09, 2011

Blast From the Past

As a child of the 80's, I have fond memories of an older generation of computers. It started with my first Nintendo Entertainment System in 1989. I learned the basics of BASIC programming on a second-hand Commodore 64. Old computers and retro games utterly fascinate me. So I reacted with utter joy when I saw that Commodore computers are back on the market. Well, sort of.

The original Commodore Business Machines was liquidated in 1994, owing to the company's inability to properly market their innovative Amiga line of computers. While the Amiga brand name and intellectual property have changed hands numerous times since then, Commodore's trademark apparently belongs now to Commodore USA. (This should make for an interesting courtroom battle with the current owners of the Amiga brand, Hyperion Entertainment.)

Commodore USA has contracted with CyberNet to produce PC's that are completely contained within the keyboard. The flagship model is their new Commodore 64, in a case designed to match those distinctive beige cases and black keys of so long ago. Commodore offers other all-in-one PC's based on existing Cybernet computers are available now; the Commodore 64 has already sold out.

The chips inside the keyboards have no lineage to the Commodores of yore (while a small but dedicated group tries to keep the Amiga platform alive on Power PC hardware.) While these new Commodores have PC hardware inside, they can run the classic Commodore software using emulators once Commodore USA finishes its "Commodore OS." If I were a betting man, I'd say that "Commodore OS" was based on the open-source port of the Amiga OS to the Intel architecture.

I'm very interested in buying a new Commodore, but the $595 price tag for the Commodore 64 without monitor seems a bit steep. After all, it only has an Atom CPU (although the NVidia ION graphics chipset puts it head-and-shoulders over netbooks with otherwise similar specs.) The "classic" Commodore keyboard design wasn't that great to begin with, and it led to terrible wrist strain during periods of extended typing. But if Commodore USA brings back the more ergonomic Commodore 64C or Commodore 128 I'd probably place a pre-order the instant they were available.

Wednesday, April 06, 2011

Building a Bigger Falcon

When Elon Musk speaks, the space community listens. Once-skeptical industry observers have to take his bold vision for the future of space travel seriously after the successful launches of Falcon I, Falcon 9, and most recently the Dragon spacecraft. With little hyperbole he's now predicting that his SpaceX team will launch Falcon Heavy, the world's largest current launch vehicle, by 2013.

If "Falcon Heavy" sounds familiar, that's because it is. The original Falcon 9 plan called for a "Falcon 9 Heavy" that would consist of three first stages in a parallel cluster with an upper stage on top. Each 1st stage booster would have nine Merlin engines, for a total of 27 engines igniting at liftoff. The mere thought of 27 engines is usually enough to give a mission assurance engineer nightmares. It draws comparisons to the Soviet N1 moon rocket, which was doomed by the complexity of its 30 first stage engines. But Falcon Heavy should be different. For starters, the N1's engines were designed and built by the inexperienced Kuznetsov design bureau. SpaceX also has the benefit of holding its rockets down after engine ignition to assess their performance before releasing it for flight.

The difference between the current Falcon Heavy design and previous plans for Falcon 9 Heavy are in the size of the payload. Falcon 9 Heavy would have competed with the current Delta IV Heavy, which currently flies about once or twice per year. But Elon Musk predicts that Falcon Heavy will now lift payloads twice as large as planned, roughly 50 tons. Among all American-made launchers, only the Saturn V and Shuttle were mightier. Why the change? I suspect it had a lot to do with the Augustine Commission's findings from 2009 that a larger launcher was needed for missions beyond earth orbit, especially Jeff Greason's belief that 50 tons was the upper limit for a single payload element. (After all, this was the approximate mass of the fully-fuelled Apollo spacecraft and Lunar Module.) This larger payload will likely be made possible after SpaceX develops its hydrogen-burning upper-stage. Stretching the first stage propellant tanks is also a possibility.

What would you do with a rocket that big? Elon Musk wants to send a manned Dragon spacecraft around the moon and back. For the wealthiest adventure seekers, shooting the moon would be the ultimate ride. Falcon Heavy would also be a key element in any effort to send humans to an asteroid, as President Obama has proposed. But in my eyes, a vehicle like Falcon Heavy opens the solar system to just about anywhere once in-space assembly and propellant transfer are perfected.