Chair Force Engineer

Monday, August 24, 2009


The biggest conclusion from Augustine 2.0 can be boiled down to one word, an unfortunately common one in the world of big-budget acquisition programs:


In short, we can't get there (the moon) from here. The "program of record," (i.e., Ares I&V, Orion & Altair,) can't be accomplished on the existing budget.

Of course there will be a political dimension to all of the fingerpointing that results from this conclusion. Critics on the left will blame Bush for not giving his vision an adequate budget. Critics on the right will accuse Obama of "throwing in the towel" in some non-existent moon race with China when he likely tells NASA they'll have to survive on their existing budget.

Plenty of fingers will point towards Mike Griffin and the people who worked directly for him, for pitching an unsustainable architecture. There's no doubt that ESAS was needlessly expensive, and plenty of cheaper alternatives existed. But Griffin's critics can't say with any certainty if their alternatives could have been fit within the existing budget. ESAS was colossally unaffordable, while something like DIRECT or EELV might have been marginally unaffordable. In the end, we're still not going to the moon anytime soon.

The one area where there's no excuse for either Mike Griffin or Sean O'Keefe is the gap between shuttle and Orion. The historical example of Apollo should have convinced both NASA administrators that capsule development would be a seven-year effort. If a contract for Orion were awarded in late 2004 (a reasonable amount of time after President Bush's January 2004 speech setting a goal of 2011-2014 for Orion,) we might have a manned capsule by 2011. Even with the Orion contract being awarded in 2006, first manned flight by 2013 would have still been realistic--if the capsule's requirements weren't continually shifting with each setback in the development of the Ares launcher. If the capsule people had a stable set of requirements they were working towards (i.e., the established performance of the Delta IV Heavy,) we wouldn't be seeing the gross schedule slips we've seen in Orion's Initial Operational Capability date up to this point.

Every time I talk to my friends within the aerospace industry, I hear the same set of doubts about why we're "wasting money" by paying NASA to launch humans into space. There's a growing sense among the public that there are diminishing benefits on earth for all the money the taxpayers spend on space activities. I'm certain that many people who used to support NASA are growing increasingly dismayed by the "competency gap." The agency has lost the ability to duplicate so many of its past triumphs.

Maybe the solution to all of NASA's ills is to hurl more money at its problems. But if the agency can't demonstrate why it can be trusted as a good steward of taxpayer funds, and why it's still relevant in the face of private-sector space programs, does it deserve the extra bucks?

Friday, August 21, 2009


The fun in a James Bond movie lies in the way it can take the classic James Bond formula and put a fresh twist on it. Example: in most Bond movies, Agent 007 saves the world and gets the girl by the end. In 1965's Thunderball, James Bond and the girl are seemingly stranded in a raft in the middle of the ocean after a climactic battle aboard a yacht. Never fear, as Agent 007 always has a gadget from Q-branch to come to the rescue. In this case, he inflates a balloon tethered to himself and his damsel. On cue, a modified B-17 swoops in and snares the hero and heroine using a cable-catcher on the aircraft's nose.

What does this escapist Bond-fantasy have to do with spaceflight? Well, it's a flashy way of demonstrating the technique of midair recovery for spacecraft. After much trial-and-error, it was perfected for snatching re-entering film canisters, descending under parachute. Mid-air recovery is one thing for tiny film capsules. It's quite another matter to attempt it with a manned capsule, or a recoverable engine module. Yet Bigelow Aerospace wants to try the former, and United Launch Alliance is proposing the latter.

In principle it's not difficult, but it creates challenges for the aircraft involved. In the case of large objects descending under parachute, the suspended load mustn't be carried too far off-center, or it will create a situation where the aircraft is fighting a steep bank. It also creates an asymmetric drag force, greatly impeding the aircraft's top speed and adding pitch and yaw tendencies. The aircraft selected for the mission will need to be capable of flying with the payload mass of the object being captured. Even still, the aircrew will notice an immediate loss in altitude and airspeed when the capture is made, as well as a downward pitching moment.

The size of the aircraft making the grab is important. Just as airplanes like the C-119 were unaffected by catching tiny film canisters, a larger airplane will be required to snag larger capsules. I can't give some kind of first-order guess as to which airplanes would be suitable for the midair recovery mission, but the Bigelow trade study will definitely give us an answer.

While avoiding a water landing is desirable, it's still a necessary contingency to plan for. In the event of an abort from existing launch sites, the spacecraft will splash down in coastal waters. A flotilla will still remain on standby, even if midair recovery is the preferred option. If a flotilla is required for launch aborts, it's worth keeping around in case midair recovery fails.

Midair recovery for booster engines is a good idea, because exposure to saltwater could be fatal to any attempts at engine re-use. It's certainly worthy of study for manned capsules, because it spares the astronauts the possibility of being exposed to frigid Atlantic waters which could potentially sink the capsule before the astronauts could be rescued. But the launch abort issue ensures that the recovery flotilla isn't going away anytime soon.

Tuesday, August 18, 2009

Cool the engines

Pratt & Whitney Rocketdyne, already busy upgrading its proven RS-68 engine on the Delta IV, may get even busier depending on which direction the Augustine Committee and the president decide to go with Project Constellation.

The current evolutionary roadmap for RS-68 goes to RS-68A, funded by DoD to improve performance for the Delta IV Heavy and eventually the entire Delta IV fleet. By upgrading the turbopumps for higher flowrates, PWR will put more injectors into the thrust chamber of RS-68A to improve thrust and specific impluse (raising from 409 sec to 414 sec in vacuum.)

NASA's current roadmap relied on a further upgrade of RS-68, the RS-68B model, for the Ares V super-booster. The NASA-funded upgrade would increase the engine's redundancy in certain systems (required by the current man-rating rules, and a focal point of the Delta IV crew-launch studies) and reducing the amount of gas that collects at the launch pad prior to ignition.

Yet the findings of the DIRECT team prior to unveiling DIRECT 3.0 may put a wrench in NASA's plans. Their studies (and apparently NASA's internal studies confirm this) indicate the current RS-68 engines will not survive the extreme heating environment nestled between two SRB's. The baseline RS-68 is ablatively cooled, and apparently only a regeneratively-cooled engine can tough it out. The DIRECT team settled for throwing away SSME's as their core engine, believing that this was more cost-effective than developing the proposed "regen" RS-68R. But as I've argued in my previous post, SSME's that are designed for low production costs will be very different from the baseline SSME.

A regen nozzle for RS-68 is simple in concept. Keep the inner mold line the same (to preserve the expansion ratio,) and manufacture the nozzle from thinner stock (since the extra thickness won't be needed for ablating away during ascent.) Mill some cooling channels into the outer nozzle, then braze a thin cooling jacket over the top. Ironically, I'd suspect that the baseline RS-68 shows slight improvement in Isp the longer it burns, because the expansion ratio increases as more material is burned off the inner surface of the nozzle. RS-68R will not experience the same effect.

The turbopumps need to be analyzed to ensure they can pump enough cryogenically-chilled propellant through the coolant channels. RS-68 already employs regen cooling in the combustion chamber, so adding it to the nozzle shouldn't be a huge challenge. Still, this may require a further upgrade beyond what's planned for RS-68A's turbopumps. Previous studies of RS-68R, with the same expansion ratio as the current RS-68, show an Isp improvement from 409 sec. to 419 sec.

RS-68R is definitely a step in the right direction for improving the engine's mass, durability and performance. Still, it falls short of the SSME's 453 second Isp. A longer, wider nozzle would improve specific impulse, at the expense of lower thrust. Regardless of whether RS-68R's nozzle ever reached the expansion ratio of the SSME, I'd never expect to duplicate SSME's specific impulse. After all, SSME makes use of the more complex staged combustion cycle, and has a much higher chamber pressure. Still, it's not unreasonable to expect an Isp around 430 seconds for RS-68R if the nozzle is redesigned to a higher expension ratio. This is an estimate for how the proposed Space Transportation Main Engine would have performed; it would have used an expansion ratio somewhere between RS-68 and SSME, had a chamber pressure between those two extremes, and used RS-68's gas generator cycle.

At the end of the day, NASA-Marshall will have some big decisions to make, and the trades should be backed up by something more substantial and detailed than a 60-day study. Will it be more cost-effective to develop expendible SSME or RS-68R? And if RS-68R is cheaper to develop, procure on a unit basis, or both, will those cost-savings be offset by the engine's lower efficiency when comapred to expendible SSME? The last metric can be quantified with the additional number of launches that will be required to put the same payload mass in space.

Tuesday, August 11, 2009

Shuttle-Derived Devil's Advocate

The Augustine Commission, appointed by the president to chart the future of NASA manned spaceflight, is looking at a variety of missions and boosters for the future direction of Project Constellation. One dark-horse concept that's gotten a lot of attention lately is a side-mount shuttle-derived rocket, which I think of as "Son of Shuttle-C." It's definitely an improvement over the existing Ares designs in terms of its development costs and schedule. But much like the rush to Ares, in which issues like thrust oscillation and air-starting SSME's were swept under the rug, it would be helpful to look at all of the challenges that will face the team developing the new rocket.

It's important to distinguish the new concept from the original Shuttle-C proposal. instead of flying the shuttle orbiter, Shuttle-C made use of a "cargo element" which looked much like an orbiter stripped of its cockpit, wings and tail. But the new design utilizes a much larger payload fairing, nearly as wide as the external tank. With a much wider cross section, the new rocket will be a "draggier" design than the existing shuttle or Shuttle-C.

Another thorny issue will be the separation between the new rocket's fairing and external tank. The fairing is supposed to jettison during ascent, with the exception of the aft thrust structure and the connected structure which supports the payload. There should be some concern about achieving a clean break when the fairing jettisons, although it shouldn't be much more dicey than when the SRB's are cast off. In the block I version of the new rocket, the thrust structure and payload structure would separate in the same fashion as the shuttle orbiter. I would guess that the payload would eject parallel to the vehicle's yaw axis, similar to the way the shuttle deploys its payloads.

The separation issue gets riskier on the block II rocket, where a live upper stage is carried inside the fairing. The upper stage ignites suborbitally at a speed just under Mach 17. I would be very concerned about recontact between the upper stage and either the payload structure or the ET.

The "Son of Shuttle-C" promises low development costs for as long as we have spare Space Shuttle Main Engines to throw away when the orbiters are retired. But the new challenge is creating a version of the SSME which can be economically thrown away after every mission. While promoted as an upgrade of the SSME, it's really an extensive new development (moreso than developing the RS-68A from the existing RS-68.)

There already was an expendible Space Shuttle Engine: it was called RD-0120, and it was developed by the Soviets for their own shuttle system. It pioneered the "channel wall" nozzle concept which would drive the production cost of SSME down if it were adopted. But do the Russians still have the tooling and industrial knowledge to build more RD-0120's? Is it practical and politically feasible to buy RD-0120's from Russia? The answer to both questions is probably "no." But it would be worth consulting with them when designing a new SSME nozzle. RD-0120 achieved a similar specific impulse to the SSME, but it required a higher expension ratio nozzle and produced less thrust.

A channel-wall nozzle, designed to the same expansion ratio as the existing SSME, can’t be developed overnight, although Wayne Hale has stated that the idea has been given some consideration in the past. Channel-wall nozzles are far easier and cheaper to manufacture than the existing shuttle nozzles, which use thousands of tiny tubes welded together to form the nozzle wall. Instead, the coolant channels are milled into a solid piece of metal, with a thin sheet of brazed over the top of the channels to seal them off.

Current Shuttle PM John Shannon also stated that the turbopumps would have to be redesigned for making a cheaper, throwaway SSME. Again, this isn’t a trivial modification. I have to wonder aloud whether it might be possible to substitute the expendable turbopumps from the RS-68 (which are designed for higher flow rates than those on SSME.)

When it comes to "Son of Shuttle-C," I don't think it's a bad idea, if your goal is to preserve the "Central Florida Economic Stimulus" that the shuttle program provides. But it will not be a trouble-free or inexpensive development; as long as NASA and the taxpayers keep that in mind, it should result in a workable launch vehicle. Everybody should be warned that an expendible SSME will be a very different beast from the current SSME, and developing the new engine may force the taxpayers to look back on the program with bitter feelings about what was supposed to be a quick and economical program to close the post-shuttle gap.