Wednesday, September 14, 2011

Uh-huh. Rocket Science

Update: Rocket buddy Ralph Schiano pointed out that the SLS is going to use Space Shuttle Main Engines, fueled by liquid hydrogen for its first stage. Any impressions I made about NASA being smart by using kerosene, please ignore. LH2 is one of the quickest moves I could think of to make this project more expensive than it ever needed to be.

Yes, I really am a rocket scientist. I have a big piece of paper on my wall with fancy lettering that says so.

The first consequence of being a rocket scientist is that I have many friends who enjoy saying, "Let me ask my friend, Jim. He's a rocket scientist and he'd know." This seems to make a lot of people happy that they know at least one rocket scientist, so I'm fine with that.

The second consequence is that every time something happens in the news concerning rockets, spaceships, astronomy, or satellites, I am asked for an expert opinion as soon as such news appears on the internet. My typical response is "the who in the what what now?" because I'm usually busy doing something else. But then I have to read up about whatever the news was and concoct an opinion, because "I dunno" is usually an unsatisfactory answer for my friends.

Today's Hot Space News Topic concerned NASA's new proposed Space Launch System (SLS), the latest in a near decade-long series of futuristic launch vehicles designed to take astronauts and equipment into deep space. NASA held a press conference, announcing the new design that featured a fat kerosene-and-LOX main stage strapped with two Shuttle-derived solid rocket boosters (SRBs). Here's a pretty artist's conception of the thing:

It looks like someone took an Apollo-Saturn V, removed the second stage, and bolted a pair of Shuttle SRBs to the stack. Wait a minute: if it already looked pretty much like a Saturn V, why would NASA bother with the SRBs? Why wouldn't they just build a newer Saturn V?

The answer is, of course, jobs, money, and politics. The New York Times estimates the cost of building two of these vehicles by 2021 would be about $62 billion That's a lot of Congressional money to kick around in the important districts of the House and Senate appropriation committee members. The primary assembly would be in Florida, the home state of former astronaut and current Senator Bill Nelson - - who also happens to be on the Budget Committee, the Committee on Commerce, Science, and Transportation, and the Committee on Finance. The solid rocket boosters, built by ATK, will be constructed in Utah, home of Senator Orrin Hatch. Hatch is the Ranking Minority Member of the Committee on Finance.

What's the big deal about having segmented solid rocket boosters on the SLS? They're an alternative propulsion system that isn't really needed. The SRBs provide extra lift to move the launch stack up from sea level, but that job could also be handled by making the main stage bigger, adding a second stage, or ratcheting the lift requirements of the launch vehicle down a bit. SRBs are built in segments - - as you'll recall, this segmentation proved to be quite a weakness in design for the astronauts onboard Challenger back in 1986. The SRBs are segmented so that they can be disassembled in Utah and shipped to Florida by rail - - that's the only reason for the segmentation. There are shorter, unsegmented solid boosters in production (Aerojet Corporation makes quite a few) but they aren't built in Senator Hatch's constituency.

Let's roll the clock back a bit and see how we wound up with this configuration. In 2003, the Space Shuttle Columbia broke up during reentry because its thermal protection system was struck by foam and ice debris during launch. The reason for the debris impacts was because of the poor design of the Space Shuttle launch system. Prior to the Shuttle, manned launch vehicles never had their reentry surfaces exposed to any launch debris. Since there was no way to protect the Shuttle reentry system from impacts, and since NASA was committed by international agreement to complete construction of the International Space Station, President George W. Bush announced that the Shuttle fleet would be retired, following the completion of the ISS construction in 2010.

As an appeasement to both Nelson and Hatch, Bush okayed a new plan for NASA called "Project Constellation," where NASA would strive to land people on the Moon, Mars, and "Beyond," wherever that was. The new Constellation program designers concentrated on reusing as much Shuttle hardware as possible, modifying the external tank, the SRBs, and the Space Shuttle Main Engines (SSMEs). This was supposed to cut down on development costs, because the technology was already in the factories and building this hardware should have been a snap.

Unfortunately, the reconfigurations didn't work, mostly due to a lack of funding by the government and a lack of foresight by NASA management. The first variety of new launch vehicles, known as Ares 1-X, was designed as a super-tall version of a single SRB, with a liquid-fueled second stage as an additional booster. A lack of budget money pushed the timeline of development back for the second stage, so NASA decided to attempt a flight of the Ares 1-X without a working second stage. The result was a disappointing suborbital launch of the Ares-1-X, coinciding with the cancellation of the entire program. Here's a pic I took of the pre-launch preparations for Ares 1-X, with the dummy second stage rising high above the old Shuttle gantry:

Ares 1-X, and the unflown Ares 1 were supposed to be the run-up to the big cargo-hauling ship of Constellation, the Ares V. Ares V was going to stretch out a Shuttle External Tank (ET) add a few SSMEs to burn the liquid hyrdogen (LH) in the ET, and two SRBs to carry the initial stack into space. The biggest problem with this arrangement is that the Ares V would continue the legacy of an LH launch fuel at sea level that plagued the Shuttle flights. Liquid hydrogen is extremely dangerous, and requires extremely low temperatures to be useful at ground level. Remember the spark generators at the base of the Space Shuttle, that would shoot a shower of pyrotechnics just before launch? Those spark generators were there to ignite any stray hydrogen at the launch tower, just so that the rocket ignition didn't detonate trapped hydrogen underneath the Shuttle. It's a really dangerous and complicated practice, and it buys little in the way of efficiencies for larger ships.

Ares V at left, Ares I on right

The new SLS system avoids LH as a sea-level fuel. Instead, the liquid fueled first stage runs on good old kerosene, the same fuel that powered the Saturn V's first stage. Kerosene is also the same fuel SpaceX is using in its deep space launch vehicle, the Falcon Heavy.

According to SpaceX, the Falcon Heavy will deliver only slightly more than 1/3 the payload of the SLS into low Earth orbit, or in other words, about 58 tons of payload. That doesn't seem to be too impressive, until you look at the cost of a Falcon Heavy - - the TOP price is scheduled for about $125 million per launch, about $31.775 BILLION cheaper than the expected SLS price tag per launch. The reason? SpaceX doesn't have to please the constituencies NASA must bow to in every price negotiation. SpaceX (and the other COTS companies) can press for cheaper prices, cheaper solutions, and simpler designs to get their product to market. Without facing competition, and being at the beck and call of irked Congressmen, NASA can't cut corners if it means trimming the fat. So, they'll continue with this $62 billion research project, maybe have one or two launches, then they'll declare success and mothball the vehicle. Don't worry, though - - its job will be completed by private companies with better control of their balance sheets.

Whew, that felt like a lot of spewing about rockets. Let me know if you have other questions about the SLS and I'll try and give you my bestest answer EVARRR in the Comments section.


  1. Yay rockets!

    Every time I see the word kerosene I think of the scene in Home Alone 2: Lost in New York where those two idiots start climbing up the rope that Kevin soaked in kerosene. Good stuff.

    If only the government's budgeting system didn't suck. It just makes me sad. Lots of space companies to work for nowadays, but I want NASA, you know?


  2. One reason I breathed a sigh of relief when the last shuttle safely launched was "no more SRBs." Those things scare me! I'm sorry to see them strapped to the sides of a stubby Saturn thanks to politics, but it has ever been thus. Purely selfishly and nostalgically, it will be GREAT to see something vaguely Apolloish back on a launch pad.

  3. To me it looks a lot like an Aries V with a Saturn V paint job.

    I'd love to see a "Saturn VI" that would use the same basic design with key updates over the last 50 years. Welding the tanks was the killer Saturn job back in the 60's, but one thing the Shuttle program did do well was develop ways to turn out Saturn-sized tankage on an assembly-line basis.

    The Shuttle needed SRBs because the SSMEs weren't powerful enough or numerous enough to get the whole stack off the pad by themselves. Here I think they're just being included for bragging rights, so the NASA admins can claim they've designed something "better than a Saturn V" out of Shuttle technology.

    Finally, as you point out, LH2 in the first stage has more than a few drawbacks. I don't completely agree that it's more dangerous -- at least not more risky than using it in the S-II and S-IVB Saturn stages. The reason the von Braun & Company selected RP-1 as the S-IC fuel is that it was much denser than LH2, so they got a lot more lift out of the same size tank by using it. Using LH2 on the S-IC would probably have required the stage to be Nova-sized.