Chair Force Engineer

Friday, September 28, 2007

Fuel for a Revolution

Rand Simberg's PopMech article on orbital propellant depots really resonated with me, particularly the part about propellants being a low-cost payload.

Let's look at the economics of the space business for a second. While launch vehicles are big-ticket items, the reality is that the satellite payloads are where the money is at. The launcher's payload is usually worth several times what the launcher costs. For that reason, most satellite operators are reluctant to build and fly space assets unless they absolutely have to; and when they have to build a space asset, they try to make it as lightweight and compact as possible.

Under the current paradigm of high-cost, low-mass payloads, there are two consequences for the launch vehicle industry. The first is that the flight rate is too low to justify the development of reusable launchers. The second is that there is no demand for heavy lifters such as Ares V.

Now let's assume that NASA adopted an orbital-refueling strategy for going to the moon or Mars, and offered commercial contracts to anybody who could deliver propellants to orbit. All of a sudden, there's a need for multiple launches of payloads that cost thousands, rather than millions or billions, of dollars. There's also a demand for large propellant masses to be delivered over a short span of time (due to propellant boil-off concerns.) And because propellant is such a cheap payload, the only thing lost in the event of a failure is the time and money that went into the launch campaign for the vehicle that just failed (which is substantial at this point in space history.)

The need to deliver low-cost propellants to orbit creates an intriguing niche in which either an RLV or a heavy-lifer could be economically justified. Studies have shown that an RLV would need to fly fifty times per year (or more) to be economically viable. Assuming the technologies to build such a reliable RLV were available, and assuming 20 metric tons of propellant being delivered in a single launch, there must exist a need for 1000 metric tons of propellant on-orbit per year. Likewise, the same propellant mass could be delivered with nine launches of the Ares V (a number that is in line with the shuttle's historic maximum yearly flight rate.)

Assuming that NASA and private industry move beyond a "two moon landings per year" mentality, the need for 1000 metric tons of propellant per year can be justified. Imagine a propellant depot in low earth orbit, serving as a waystation between the earth and moon. A reusable launcher would deliver crews and/or propellants to a small space station equipped with a large propellant depot. The crews would use the space station as a point to board and refuel the craft that will take them to the moon and back.

Taking that concept one step further, a similar space station & tank farm could be set up at one of the Earth-Moon Lagrange points. A crew would transfer from their in-space transfer craft to a dedicated, reusable lunar lander. The landers would take on oxygen and perhaps hydrogen at the Lagrange Point space station. Some of the landers would be dedicated to ferrying oxygen and perhaps hydrogen extracted from the moon to the tank farm.

If humans are to become a space-faring society, it seems that we should embrace and perfect techniques like orbital refueling, instead of running away. Nobody is foolish enough to drive cross-country without making a few stops for gas along the way. The exploration of space should be no different.

Saturday, September 22, 2007

Chariot of the Sun-God

Project Apollo was a major milestone in human history. To all who have ever tried to achieve the impossible, in the face of overwhelming adversity, Apollo represented the pinnacle of mankind's achievement in all endeavors, both political, technical, and even military.

With that being said, Project Apollo is still the meterstick by which we measure great achievements. As long as we have this mentality, we will probably never be able to surpass the greatness of Project Apollo. Even though the Vision for Space Exploration has an even more ambitious goal than Apollo did (four astronauts on the lunar south pole for seven days, vs. two astronauts near the lunar equator for three days,) it's still referred to as "Apollo on Steroids."

At the same time, it should be remembered that Project Apollo was a crash program that was meant to put an American on the moon before the end of the sixties, and preferably before the Soviets did. Project Apollo was not conducted with the goal of sustainability in mind. Thus, while there are plenty of lessons to be learned from Project Apollo, we are wise to avoid a too-literal recreation of that admittedly-stupendous feat.

I am reminded of the landing mode debate from 1961-62, in which Lunar Orbit Rendezvous eventually won. At one point, von Braun and his supporters favored Earth Orbit Rendezvous. One EOR scenario would have used two rockets smaller than the Saturn V (such as the Saturn C-3) and involved propellant transfer between the two spacecraft that would be launched into earth orbit.

At the time, EOR was rejected because NASA didn't want to attempt propellant transfer while on-orbit. Given the schedule concerns of 1961-2, this was the correct decision. Today, the rejection of propellant transfer can't be justified. Using President Bush's 2020 lunar landing date as a goal, we have thirteen years to develop the systems that will take us there. That is plenty of time for us to pioneer on-orbit propellant transfer. It's already been done on Orbital Express. It can be taken a step further by modifying two Centaur stages to perform the first-ever cryogenic propellant transfer in earth orbit, then launching them on two Atlas V's.

Project Apollo had the development budget to create two very different launch vehicles: Saturn IB and Saturn V. NASA has followed suit by developing the Ares I and Ares V. However, the NASA of the 60's could not sustain production and operations for their two launchers. I believe that today's NASA is naive to think that they can succeed in sustaining two separate launchers when Apollo failed in the same arena. Had Project Apollo embraced a single launcher, the Saturn C-3, the outcome might have been different, and we might still see Saturns flying today.

The TeamVision plan for exploring the moon, Mars & beyond embraces propellant transfer. It also embraces a launcher that can be configured for both space station and lunar (EOR w/ propellant transfer) missions. Saturn C-3 could have served the same function, launching manned craft and propellant tanks for an EOR lunar mission in its three-stage version, or by launching Apollo capsules on earth orbit missions in a two-stage version.

The question NASA must address is whether it will continue to worship the sun-god Apollo, or whether it will blaze a new trail that learns from both the successes and failings of the sun-god. I do not believe that NASA has critically examined all of the factors that made Apollo unsustainable after achieving the initial goal of beating the Soviets to the moon.

Friday, September 21, 2007

Hybrid Theory

Over at Transterrestrial Musings, Rand Simberg speculates that Scaled Composites might switch to a LOX-Solid hybrid, or a purely-liquid engine, for SpaceShipTwo. While I believe that both are good ideas, I don't expect either to come to fruition.

I studied hybrid rockets extensively as a senior in college. As a result, I came to question the benefits of hybrid rockets. True, the motors are simple, the propellants are cheap, and the ground handling of the fuel is much safer than a traditional solid rocket. As far as I can see, the benefits end there. Specific Impulse is low, and does not exceed solid rockets unless cryogenic liquid oxygen is used as an oxidizer.

Why choose a hybrid over another propulsion system such as a simple, pressure-fed liquid rocket? I tend to think that most hybrid proponents are people who are afraid of handling cryogenic liquids. These hybrid proponents insist on using non-cryogenic oxidizers like nitrous oxide; this may make the rocket marginally safer than a LOX-solid hybrid, but it dramatically reduces the specific impulse of the rocket motor.

I disagree with these people (probably including the likes of Burt Rutan) who feel that cryogenic propellants are too unsafe to use for space tourism vehicles that will fly on a weekly basis. In the Air Force, it's routine to see 19-year-old Airmen who are fresh out of tech school and loading liquid oxygen into military aircraft. I see no major obstacles towards using LOX-Kerosene for space tourism vehicles.

If Scaled Composites cannot pinpoint the cause of the tragic nitrous oxide explosion that claimed the lives of three employees, I still don't foresee Burt Rutan & co. giving up on nitrous hybrid systems. Instead, they'll be talking to SpaceDev or Environmental Aerosciences Corporation (the two vendors who competed for the SS1 motor, with SpaceDev developing the successful flight motor,) to join in on the SS2 motor development.

Thursday, September 20, 2007

AIAA Space 2007, Day 3

Today was a slow day. Not too many people (besides the grammar schools) visited the exhibit area. The booths closed up at 2 PM, so I went home after we tore down. I didn't go to any of the presentations in the afternoon.

Previously, I had heard a rumor that a prominent Orbital Sciences employee has traditionally brewed special batches of beer, which he would share with others after every successful OSC launch. Today I had the opportunity to speak with the gentleman in question. Our primary topic of discussion has nothing to do with the "Taurus-2" concept, or with responsive spacelift. It was about the beer rumor. Unfortunately, the truth pales in comparison with the rumor. The special beer was only used to celebrate the inaugural Minotaur I launch.

During the course of this trip, I learned a very valuable lesson. When attending a conference in southern California, ALWAYS get a room in the hotel closest to your conference location. I stayed 12 miles away, and the horrendous SoCal traffic meant that my drive to the conference could take as long as an hour.

I spent a quaint and quiet evening in Seal Beach. The city is steeped in Apollo and Delta tradition, but I spent my time merely taking in my first views of the Pacific Ocean and eating at an Irish-themed restaurant. It was a lovely way to end a sorely-needed trip away from the office.

Wednesday, September 19, 2007

AIAA Space 2007, Part 2

As impressed as I was with the first day of the AIAA's yearly space conference, the second day made the first pale in comparison.

Working the booth in the exhibits area consisted of much of the same swag-peddling as before. Trying to explain hyperspectral imaging to the third-graders who were on a class trip to the conference proved to be very difficult. We received less dignitaries at the booth as we did on the previous day. I did get to talk to members of the contractor teams I've been working with on my day-to-day job. I also met a lot of great folks who now work as experienced members of industry, but used to be junior officers in positions similar to mine.

The most interesting visitor was an eccentric gentleman who wanted to know about what work my unit was doing in the field of "anti-gravity research." I told him that I wasn't aware of any of that research going on; he probably thinks that I'm part of the "Area 51 conspiracy." I should have told him to bother DARPA, since they're the guys who do real research into "mad scientist" ideas. I wish we really did have a means of cheating gravity and building flying saucers, but we're unfortunately grounded by physics.

The exhibitors have been served boxed lunches (and fairly lavish ones, by my standards) by the convention center in Long Beach. But I received a complimentary ticket to the awards luncheon that would include all of the conference's VIP's. I think the gravity of the event sank in when I saw name placards like "Michael D. Griffin" and "Elon Musk" at the head table. I sat in the back of the room, but even still, I was sharing a table with none other than Vladimir Titov (probably the most accomplished cosmonaut to have flown during my lifetime.) I was far too intimidated to speak with him; I spent my lunch watching my table manners, avoiding embarassing faux pas, and trying to be on my best behavior.

The awards segment of the luncheon was brief. Burt Rutan accepted his "Engineer of the Year" award and made some brief remarks that were humble and somewhat moving. The XSS-11 team received a well-deserved award for accomplishing the most spectacular space mission in the history of Air Force Research Lab; sadly, the names of several engineers who made the mission possible were omitted from the awards program. Their efforts will not be forgotten by those who are knowledgeable on the subject of XSS-11.

Administrator Griffin gave the keynote address, and moved the audience with several anecdotes: how the gift of a book on stars as a child turned him into a lifelong space enthusiast, how the afforementioned book was clandestinely flown on STS-114, and how people came from far and wide to see the space shuttle when it made an unexpected ferry stop at Rick Husband Airport in Amarillo, TX. He contrasted the first 50 years of space with the first 50 years of aviation and noted that, by this point in aviation's history, air travel still wasn't commonplace like many of us expected spaceflight to be. Lastly, he remarked that the problem with the government-industry balance in space has not been too much government, but too little industry. The question and answer session ended without anybody getting tasered, so I was pleased.

The afternoon presentations were quite interesting. A group from Space Works Engineering talked about a concept for manned Mars missions. The result wasn't as rosy as Bob Zubrin would like to hear. SpaceWorks predicted four Ares V and one Ares I launch per Mars mission, a crew of only three, a fairly high loss-of-mission rate, and a cost of $100 billion for development of Mars-related hardware and launch of the first four manned missions. When the report becomes publicly available, I'll have more commentary to offer.

Dr. Chauncey Wu had an exceptional presentation on lunar lander designs that had been generated at NASA-Langley. The two preferred concepts were DASH and "Cargo Star." The former would make a horizontal landing and utilize a "lunar crasher" stage. The latter would land in a horizontal configuration, but would require the Orion capsule to transpose from an axial to a transverse position prior to the lunar orbit insertion burn. I'm not too fond of "lunar crashers" because they require extra development over the Apollo "ascent & descent" stages, they contaminate the lunar terrain, and they do not lend themselves to future reliability. Then again, they lend themelves well to shorter vehicles that are easier for a human pilot to land. They key takeaway from his study was that the lunar lander concept and its payload fairing are still nebulous, and the final result will probably surprise a lot of people.

Dr. Allison Zuniga gave the last presentation on Constellation design cycles. It was heavy in program management jargon, but there were still some interesting takeaways. NASA is trying to find ways to add capabilities back to the system, after stripping certain ones away to save mass. For instance, the loiter time of an EDS in earth orbit has shrunk from 90 days to two weeks; hopefully the Ares I&V can be launched within 90 min of each other, but the reduced loiter time is still a major concern. She still maintained that Orion will land on terra firma, while the young JSC engineer from the previous day claimed that the "land-vs-water landing" trade study was still ongoing. Dr. Zuniga still used the Orion 606 configuration in her charts, even though images and details of Orion 607 have been on the internet for weeks. Most troubling, NASA is currently looking at changing the load paths so that the lunar lander will not be crushed when the J-2X ignites to push Orion and the lander to the moon while stacked with the EDS. This issue is by no means a cause for worry, but I'm surprised it hasn't been addressed sooner.

It's great that the lunar lander issues are bing discussed at this point. If the people working these issues are reading this post, I have a few comments I'd like to offer up:
--The lander will necessarily be taller and heavier than it needs to be, as long as NASA requires the lander to perform the lunar orbit insertion burn. The descent tanks will be larger than needed for the descent phase of the mission, and the extra mass & volume will be lugged down to the lunar surface. If the Orion service module was big enough to perform the LOI burn, the extra tank mass could be left in lunar orbit; but this would require more performance out of the crew launcher, and Ares I just doesn't have what it takes to do it.
--I still haven't seen how NASA plans to pump the liquid oxygen and hydrogen into the lunar lander descent stage. I assume they'd do it after the lander is encapsulated in its fairing, but that will require a means of attaching the propellant fill lines to the Ares V launcher and pumping the propellants into the encapsulated lander.

AIAA Space 2007, Day 1

I wanted to encapsulate my impressions of the AIAA Space 2007 conference in a neat little package for the benefit of this blog's readership. I think the best approach is to offer daily summaries, so here I go again.

I spent the majority of the first day in the exhibitor's area. In the course of doing so, you get to meet all sorts of interesting people. Some of them are the movers and shakers within the industry, government and academia. Others are well-known names from websites and internet forums. Some of my visitors included Don Nelson and Dennis Wingo. We also entertained the president of AIAA and an Air Force Major General.

Plenty of people want to hear what you have to say about your organization. Others (like the schoolchildren who get to tour the conference) only care about the free swag that the exhibitors have to offer.

I sat in on a few presentations at the end of the day. One of the more interesting ones was given by a young engineer (I would say he's been out of school for a year or less) at JSC. He talked about a potential subscale demonstrator that would validate the Orion heatshield (an area of particular concern, in my view.) One test flight would examine a ballistic return at lunar mission velocities, while the other would demonstrate the skip-landing approach. The ability of the skip-entry technique to extend the downrange landing distance was discussed, but I still have questions about how skip-entry can be used to extend the crossrange capabilities of the spacecraft. Overall, the proposed heatshield test program could be accomplished for $165 million (including two Minotaur IV launches,) but the funding availability looks iffy at this point.

The last presentation of the day (and most eagerly-anticipated, in my view) came from Stephen Metschan of TeamVision. The topic was the DIRECT 2.0 launch vehicle plan and how it fits into TeamVision's five-spiral approach to exploring the moon, Mars and beyond. The paper that accompanied the lecture is over 130 pages long, but I'll summarize the key improvements (in my view) over the previous versions of the work done by the DIRECT team and TeamVision.
--The preferred lunar architecture uses two launches of the Jupiter-232 vehicle
--Propellant transfer between Earth Departure Stages is now completely embraced as a part of the architecture
--High launch rates for the DIRECT launchers are encouraged; even if manned spacecraft aren't ready to fly, the orbiting of fuel-laden EDS stages can be useful for upcoming missions.
--TeamVision/DIRECT forsees a speedy transition from initial sortie missions to the building of infrastructure at the Earth-Moon LaGrange points and use of reusable (up to eight missions) landers between the EML points and lunar surface.
--According to their studies, NASA's current architecture does not have adequate margins to launch the propellant required for access to all latitudes on the moon. DIRECT rectifies that problem through the use of two Jupiter-232's per mission. It should be noted that although NASA has specified a requirement for access to all latitudes, it has indicated that the lunar south pole is its preferred destination (requiring less propellant than the mid-latitudes.)
--The DIRECT launchers are adequate launch vehicles for a Mars mission based on the Design Reference Mission 3.0 architecture. The moon will serve as a testing ground for elements of the Mars hardware.

From this point on, it's hard to say what will happen to the work that's been accomplished by TeamVision and DIRECT towards making the Vision for Space Exploration more affordable and sustainable. Perhaps the issues they've identified with NASA's architecture can be surmounted, and NASA will charge ahead. It's just as likely that technical problems and shrinking budgets will put NASA on a collision course with Congress. Regardless of what happens, I think that fresh thinking on the topic should always be welcomed.

Thursday, September 06, 2007

Fly Away Home

One of the challenges in building a fully reusable launcher is the recovery of the spacecraft's lower stage (or stages.) Analytically, it's easily demonstrated that a reusable launcher will probably have two or three stages. (A single-stage vehicle would place a horribly tiny fraction of its liftoff mass into orbit, and probably isn't even feasible with contemporary structures and propulsion technology.) But the booster recovery problem is much more difficult than it initially seems.

The most mechanically simple technique is to recover the boosters with parachutes. They'd either splash down in the ocean, or make an airbag-assisted landing on terra firma. The space shuttle SRB's have demonstrated this technique over a hundred times. Our operational experience with this method has taught us much about why we need to find an alternative. The cost of the recovery fleet is considerable. So is the cost of tearing each booster down between flights, shipping it to Utah and back, and reassembling it.

Parachute recovery shouldn't be completely rejected, although there's admittedly a lot riding against it. Rocketplane-Kistler hopes to avoid a lot of the shuttle SRB's problems by bringing the first stage of their K-1 to a landing on dry ground. Assuming that you have a large, open area in your predicted drop zone, I can see the Kistler approach working fairly well. Instead of relying on NASA's SRB recovery flotilla, Kistler could lift the booster with mobile cranes and haul it away on a flatbed truck. It also solves the problems associated with protecting the delicate parts of a liquid-fuel rocket from corrosive seawater.

The next best approach is the flyback booster. Buzz Aldrin's company, Starcraft Boosters Inc, has done a lot of work in this field. One of their important conclusions is that a booster staging at speeds under Mach 3.3 has enough energy to glide back to the launch site; a booster burning out at Mach 6 would require turbofan engines to return to base, but its aluminum heat-sink airframe could survive the expected heating.

In the 1960's, Max Faget's "DC-3 Shuttle" concept made use of a single, very large, winged booster. His proposed craft would have a manned crew, and retractable turbofan engines. The booster would exceed Mach 10 before burning out and falling away. It would have required heavy heat shielding based on its mission profile. The booster could be recovered downrange, then refueled with kerosene and flown back to the launch site like a conventional aircraft.

One idea I've been toying with is a very large booster with a very high staging velocity. How high, you ask? Well, high enough to fly an "Abort Once Around" trajectory and return to the launch site after a single revolution of the earth. The structural requirements and payload inefficiencies of such a booster would be nearly as bad as for a rocket that went to orbit with a single stage. The associated second stage/orbiter would be very tiny in comparison to the orbiter. Yet it has some operational advantages, such as the ability to land without turbines.

How do we proceed with the development of an RLV from here? I think that the StarHawk concept from Starcraft Boosters is a logical first step. The Air Force, under the banner of "Responsive Space Access," should take the lead on this program. While Aldrin's company doesn't have the ability to take lead in building the booster, the Air Force should keep them onboard in a consulting role, and contract the detail design and construction of the booster to the established aerospace firms. StarHawk should even be designated as an "X-Plane."

Building a modest flyback booster like StarHawk will give the US government and industry a lot of experience in designing, building, and operating a reusable lower stage booster. That experience can be shared with the industry and leveraged to build even bigger flyback boosters for rockets that will truly open the space frontier.

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Wednesday, September 05, 2007

No Chance Outside

There's an old Air Force joke that "NCO" doesn't stand for "Non-Commissioned Officer." It stands for "No Chance Outside." The point of the joke, as best I can tell, is that the master sergeants have spent so much time in the Air Force that they can't imagine doing anything else in the private sector.

Luckily for most members of the armed forces in the era of contracting out many jobs that used to belong to uniformed personnel, it's quite easy to take off the uniform and get paid much more money to do the same thing as a contractor or government civilian that they were previously doing when they were on active duty.

At the same time, the situation is much more harsh for people who don't like what they were doing while in uniform and want a change of profession. By most accounts, the retraining that the military offers to separating personnel is not very good. I speak with friends of mine (like the guys with engineering degrees who were forced into the communications field) who share many of my fears and insecurities. While they may want to leave the Air Force, they have no idea what they're going to do on the outside. All they know is what they've been doing for the last few years while wearing the uniform. I suspect that many of them will stick with the Air Force because it represents stability and security in their lives. Many of them will find enjoyable assignments, and some will advance to the upper echelons of the military hierarchy.

Of all the general officers in the United States, the majority of them will tell you that they wanted to leave after their first tour. Many of them wanted to leave after subsequent tours as well. But something kept calling them back, and they eventually found assignments they liked. While many generals are too humble to admit it, they also had the wisdom to make smart choices during those years of struggle in order to achieve the rarefied ranks.

The alternative to the "No Chance Outside" mentality is the "Make it Work" mindset. Whatever happens, these individuals have the resolute faith that they can make things work out in the end. Some of them are resourceful and strong-willed, and they will make it happen. As for the others, I think they are the ones who comprise the group we know as the stereotypical homeless veterans.

I used to embrace the "No Chance Outside" mentality. I can think of a crucial moment in my life, just over five years ago, when I firmly embraced "No Chance." After an entire lifetime of parental smothering, I had to look ahead to what life would be like when I was finally set on my own. I thought that the regimented lifestyle of the armed forces would help me in that regard.

In hindsight, everything I believed five years ago was wrong. The heavily-regimented lifestyle is applied to the junior enlisted, but not to the officers. You can't succeed as a military officer if you don't express a high degree of independence and assertiveness.

At the same time, everything I needed to learn, I mostly learned from college. Much of the rest was picked up in my first few months living on my own after commissioning. Going to college with half the country between the student and the parents is the best remedy for a child who has been suffocated by overprotective parents for eighteen years.

In five years time, I've rejected the sense of despair from having "No Chance Outside." I will learn to make it work. I'll even take jobs working retail if I have to. And if I fail, then I at least failed in trying to assert myself on my own, and trying to live the American dream. To fail is to earn a spot in the next "Bumfights" video. I'll be the guy fighting a toothless vagrant over a stale turkey sandwich.