More undead satellites

Roamy here.  I’m always fascinated by how some spacecraft really exceed their designed lifetime.  Here’s two satellites that not only finished their original mission but had enough fuel left over to go do something else.  Two of the THEMIS satellites studied Earth’s magnetic field for two years then were moved to study the Moon, especially the wake the Moon leaves in the solar wind.  The two satellites were renamed ARTEMIS for Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun, which shows NASA can come up with an acronym for anything.  They are currently at the L1 and L2 Earth-Moon Lagrangian points, which is where gravitational pulls between the Earth and Moon cancel each other out.  The article says these are the first spacecraft for these orbits, though NASA has sent spacecraft to the Earth-Sun Lagrangian points before.

In April, they will elongate the orbits to get closer to the Moon and  get even more data on what happens to the Moon’s surface when it passes through the Earth’s magnetic field.  Their mission is currently planned through 2012.  Pretty good for two satellites described as “dead spacecraft walking”.

Zombie satellite recovered

Roamy here.  Cosmic rays and high energy protons can do strange things to electronics on spacecraft.  Latchups, burnouts, and data errors are all filed under the category “single event effects”.  Think of it as getting the Blue Screen of Death on orbit.  When the spacecraft is communicating with the operators on the ground, usually it can be recovered.  For example, the Spirit rover on Mars was stuck in a reboot loop (scroll down to January 23, 2004) where it rebooted itself more than 60 times in three days.  It turned out to be a problem with the flash memory onboard – it was reformatted, the problem went away, and the science mission continued.  Spirit rebooted itself a couple of times in April 2009, but given how long it’s lasted on Mars, no one seemed too surprised by that.  NASA report RP-1375 has a pretty good list of the satellites recovered from single event effects (Intelsat K, Anik E-1), the ones that were recovered but had a shortened lifetime (Anik E-2, GOES-7), or were completely lost (GOES-4, DSCS-II).

Now take the case of the Galaxy 15 satellite.  It lost contact with the ground last April but kept broadcasting signals, interfering with other satellites.  Finally, last month, the batteries ran down enough for it to go into safe mode and start listening to the ground again.  It should be able to go back into service and hopefully not have a shortened lifetime.

Y’know, if you have to take a zombie down, double-tap.  (reference link)

For want of a nail

Roamy here.  On Christmas Day, the Indian Space Research Organization launched their GSLV, or Geosynchronous Satellite Launch Vehicle.  It didn’t get very far.

[youtube=http://www.youtube.com/watch?v=xXUIFZjDMuc&fs=1&hl=en_US]

Spaceflight Now reports that a group of ten cable connectors snapped, rendering the control system useless.  The rocket went off-course, and, well, you see what happened.  Cable connectors seem like something easy enough, but launch vibrations or unknown stress may have been too much for them.  (Test what you fly, fly what you test.  Just sayin’.)

NASA learned the harshest lesson in electrical wiring with the Apollo 1 fire.  There were a lot of design flaws in the capsule, including the hatch design, the pure oxygen environment, and lots of flammable materials, but post-accident investigations pointed to a spark from a short circuit being the probable culprit.  Poor wiring, poor connections, wiring insulation abraded off in places, etc. – one of those led to three good men dead. 

Thankfully, all that was destroyed this time was a communications satellite.    ISRO should be able to figure out where it went wrong and fix it.

Spacesuit traveling exhibit

Roamy here.  As much as it annoys me to link the New York Times, this article about the Smithsonian spacesuit collection is pretty good.  I had the pleasure of meeting Ms. Young, the now-retired curator of the spacesuit collection, a few years ago.  She is the author of  Spacesuits: the Smithsonian National Air and Space Museum Collection, a book I highly recommend for space junkies like me.

She was very helpful in identifying some of the problems with the spacesuit materials – in particular the crumbling rubber and the polyvinyl chloride plastic that, over the decades, degraded into something truly foul-smelling.  Because of different materials used, the older Mercury suits were in better shape than the Gemini suits. The Smithsonian collection also includes suits from the X-15 test program, but the article doesn’t mention whether those are part of the traveling exhibit.

In looking at designing space suits for long-term use on the moon, we had to remember that the spacesuits designed for Shuttle and International Space Station use are much heavier than the Apollo-era suits.  The Apollo suits only had to last a few days, not for years of thermal cycling, radiation, and micrometeoroid hits, plus the added problem of lunar dust going where you don’t want it.  A future astronaut has enough to worry about without having to climb into a funky-smelling suit.

UPDATED:

Jim Irwin's suit from Apollo 15 (and Mini-Roamy) at the Smithsonian Udvar-Hazy Center

The Apollo crew that almost died

Roamy here.  You saw the post title and thought Apollo 13, right?  Let me tell you a NASA story you may not have heard.

The Apollo-Soyuz Test Project was an idea floated after Apollo 11, for peace in space between the Americans and the Soviets.  It flew in July 1975, with Tom Stafford, Vance Brand, and Deke Slayton for the American crew, Alexei Leonov and Valeri Kubasov for the Soviet crew.

Crew with full-size mockup of Apollo-Soyuz

Deke Slayton was the last of the original Mercury 7 astronauts to finally fly in space.  A heart rhythm problem had grounded him earlier.  Tom Stafford had flown on a couple of Gemini flights and flew  this >< close to the moon on Apollo 10.  Stafford also served as a pallbearer for the Soyuz 11 crew (story for another post), so the Soviet cosmonauts knew him pretty well.  And you should know that Alexei Leonov was the first man to walk in space.

Leonov on right "Is space borscht! Is good!" Stafford on left "It's not Texas barbeque."

The mission went as smoothly as could be expected – the two launches only a few hours apart, docking without a hitch, pictures of the historic handshake in space.  There were some experiments performed in space that would be the last ones until the Space Shuttle flew six years later.

Space noogies?

Where everything started to go wrong was during re-entry.  A switch for the hypergolic reaction control system (steering) wasn’t thrown, so the lines stayed open.  When the Apollo capsule dropped below a certain altitude, a vent automatically opened to allow in fresh air, but it was close enough to the guidance system to let in a cloud of highly poisonous nitrogen tetroxide.  Stafford wrote in his book We Have Capture that they had a very hard landing and ended up upside-down.  He had to unbuckle to get to the oxygen masks, they were all coughing, and Vance Brand passed out from the fumes.  Once onboard the USS New Orleans, the usual welcoming celebration was cut short and the crew hustled to sick bay.  The ship sailed immediately to Hawaii, “the whole ship shaking as they put the power to it.”  All three astronauts had edema in their lungs (chemically-induced pneumonia) and needed two weeks to recover enough to fly back to the States.

On a good note, X-rays of Deke Slayton’s lungs showed a precancerous lesion (not accident-related), so it was caught in time.  They were very lucky to have survived the hypergol exposure.  It was the last spaceflight for Stafford, Slayton, and Leonov.  Kubasov later commanded the Soyuz 36 mission, and Brand commanded three Shuttle missions.  One interesting note: Deke Slayton was the oldest astronaut to have flown at the time of Apollo-Soyuz, and Vance Brand became the oldest astronaut when he flew STS-35.  (John Glenn is the current record-holder, and I think that will stand for a while.)  I am personally indebted to Vance Brand for a materials experiment flown on STS-5 and the ASTRO-1 telescopes flown on STS-35.

Waaaaaaay out there

Roamy here.  I saw this article yesterday, and it made me think not only of Voyager but also Pioneer 10 and 11 and wonder where they are at today.

Pioneer 10 went silent in 2003, after travelling 7.6 billion miles.  The last communication from Pioneer 11 was 1995.   Voyager 2 was actually launched before Voyager 1 and is travelling slower – it’s now 8.8 billion miles from home. Voyager 1 has been the farthest manmade object from our sun for some time – 10.8 billion miles.

If I’m doing my math right, that means it takes over 16 hours (16 hours, 7 minutes, 44 seconds for you Spock types out there) for a radio signal to travel that distance.

In terms of longevity, the Voyager probes still have to last a couple more years to beat Pioneer 6.  Pioneer 6 was a probe for studying the solar wind, cosmic rays, and space weather, and it was still sending signals (at 16 bits per second) after 35 years in space.

Space debris impacts on the X-37B

Roamy here.  XBradTC shared this article with me, which, in turn, points to this Defense News article.  Money quote is

The only physical damage seen so far has been seven areas where space debris collided with the aircraft. It also blew out a tire upon landing.

My gut feeling on this is that the seven impact areas are of the type easily seen with the naked eye.  It’s hard to guess how many impacts are probably on the X-37B, not knowing what the orbit(s) was, but after 244 days in space, there should be dozens of very small impacts on the millimeter scale.  Some of these would be hard to see without a microscope, others would be hard to see in the tile material used for thermal protection.

Nick Johnson, the space debris expert at JSC said here that the Hubble Space Telescope gets around 5 impacts per square meter per year, and that was back when the space debris levels were less than half of what they are today.  The original solar arrays for Hubble had 3,600 impacts after 3 years in space.  The Long Duration Exposure Facility (LDEF), which flew in a lower orbit than Hubble, had 34,000 impacts after 5.7 years in space.

Every one of those black dots on that 3′ x 4′ rectangular silver/Teflon blanket is an impact, and there’s about 300 of them.  You might say, Roamy, what’s the big deal?  Those are little!  You’d be right in that those aren’t going to cause major structural damage, but that one in the upper right was nasty, and they do add up.  Remember, this was flying at a time when the Space Shuttle was grounded after the Challenger accident and the orbital debris environment was much less severe than it is now.  Think about an astronaut that could get hit, a window that could crack (the International Space Station has triple-pane windows for that reason, and the Cupola has window covers), a telescope mirror, a reconnaissance sensor, a CCD camera.  This is a photo of the hole made in the composite high-gain antenna on Hubble.

That’s about three-quarters of an inch in diameter, in a quarter-inch thick honeycomb composite.  Not the same as a car-door ding in the parking lot.

Commercialization of space

Roamy here.  Okay, I’m not talking about $20 million to buy a seat on a Soyuz.  I’m talking about SpaceX and the successful launch of the Falcon 9 rocket today with the Dragon capsule for payload.

[youtube=http://www.youtube.com/watch?v=0FSiOJKKmLA&fs=1&hl=en_US]

This has been partially funded through the Commercial Orbital Transportation Services program, which you have to admit, has had more success than the Ares rocket program.  The first Falcon 9 launch was in June; today’s looked pretty good.  It’s always nice to hear “all systems nominal” for a launch and to see a good stage separation.

The Dragon spacecraft has a cargo version for resupplying the International Space Station, due to be tested next year, and, eventually, a capsule version for a crew of seven.  The parachute system and guidance systems worked – the capsule landed within 800 meters of the target, and the retrieval ship was there within 20 minutes.  I’m looking forward to hearing how well the heatshield on today’s test vehicle held up.  Instead of space shuttle-type tiles, the heatshield is made of  PICA, or phenolic impregnated carbon ablator, and I’ve had some experience with that.  It’s been used successfully on the Stardust spacecraft.

SpaceX’s competitor for commercial space flight is Orbital Sciences.  The Cygnus cargo resupply vehicle is slated to launch on a Taurus II rocket next year.

Lesson learned

Roamy here.  NASA had a great deal of egg on its face after finding out that an error during mirror polishing messed up the Hubble Space Telescope.  Hubble did go on to become a national treasure in astronomy and cosmology.  (minus 1,000 points if you think cosmology has anything to do with mascara and eyeliner.)

One of the lessons learned was to have a full test of any mirror, through the full thermal cycle, on the ground before flight, to catch any alignment problems.  Rule of thumb for thermal cycling in space is +250 °F to -250 °F, but there are worse extremes, and I’ll let the thermal analysts handle that.  Imagine going from a fairly hot oven into near liquid nitrogen temperature ( which is actually −321 °F for the pedants out there).  Coefficient of thermal expansion really has an effect, especially in assemblies where it’s mismatched.  And this is my personal view, but one test is worth 100 analyses.

NASA was determined not to have any mirror alignment problems with the Chandra X-ray Observatory, and they modified an existing facility at Marshall just for that.  Originally called the X-Ray Calibration Facility, now it’s called the X-ray and Cryogenic Facility after it was upgraded for much colder temperatures.  Either way, it’s still the XRCF.  There were 550 heater panels processed for the XRCF, and I could bore you silly with the details.

X-ray source on the upper left, vacuum tube, vacuum chamber and clean room where you put your mirror assembly on the right.  The mirrors for the James Webb telescope are being tested now. Here’s a pretty good article about it.

Test what you fly, fly what you test.

Bulletproofing a space station

Roamy here.  So I’ve talked about bulletproof vests and space debris, it’s finally time to talk about shielding.  A common way of testing different shielding designs is a two-stage light gas gun.

Your gun might be bigger, but mine shoots faster.

A high-speed rifle can shoot around 1.5 km/sec; a light gas gun can shoot up to 8 km/sec.  The “light gas” part comes from using either hydrogen or helium in the first stage.  A really good explanation of how this works can be found here. Basically you blow up some gunpowder, which moves a piston, which compresses the light gas behind an aluminum disk machined to burst at a specific pressure. Disk bursts, moving the projectile down the barrel to the target, past X-rays and/or cameras so you can figure out the speed, then impact.

Shielding for space debris is based on the Whipple shield, where you have a sacrificial plate to break up the debris into smaller particles.  (Dr. Fred Whipple, not the “don’t squeeze the Charmin” guy)  For the Space Station, you also have a thermal insulation blanket made up of thin layers of metallized plastic film and netting spacers.  A lot of thought goes into how thick the sacrificial plate should be, the spacing between all the components, and how to replace it on orbit when it’s done its job.

If you have just a sacrificial plate of aluminum and a thermal blanket, you can still get this kind of damage.

Sorry for the poor quality, but it was the best I could find that was cleared.
Add in a blanket like a bulletproof vest – Kevlar and Nextel or other aramids and ceramic cloth, and you get some dimples and craters instead.
L to R, sacrificial plate, protective blanket, simulated pressure wall

That little marble in front of the protective blanket in the picture above?  One of those fired at 6.7 km/sec is what caused that damage.  Remember from your physics class, kinetic energy equals one-half mass times velocity squared.  Only one gram or so, but that velocity squared is a bitch.

Update by XBradTC: Basically, NASA engineers are facing the same problem that every tank, bullet-proof vest, and warship designer faces- the balance between weight, protection and likely risk.

It would be the simplest thing imaginable to protect an infantryman from head to toe against small arms fire. The problem is, the weight needed to protect him would leave him immobile. An infantryman who can’t move isn’t an infantryman anymore. So risk becomes a factor. For a soldier that will spend most of his time in a Humvee, it’s pretty easy to justify adding a groin protector and deltoid armor. But a troop who has to ascend and descend steep mountains all day in Afghanistan can’t really hump that extra armor. The risk of sustaining a non-lethal wound to extremities becomes acceptable in that case.

Same thing with tanks. Tanks are more heavily armored on the front slope than elsewhere, because that is where they are most likely to be hit by the most dangerous projectiles.  You can’t armor something so heavily that it is invulnerable without sacrificing the mobility of the tank to a degree that renders it useless.

In NASA’s case, it costs a lot of money for every pound lifted into orbit. Without any protection, you face an unacceptable risk from small impacts. But with too much mass devoted to protection, you sacrifice lifting up the resources that are the whole point of the project.