BLAST High Altitude Telescope Launched

Xandu writes "BLAST, the Balloon-borne Large Aperture Sub-millimeter Telescope, was launched on the 11th at 11:09 UTC from Esrange in northern Sweden, and is currently floating over Greenland. BLAST is a 2700kg telescope with a 2 meter primary mirror that hangs from a 1.1 million m^3 balloon floating at an altitude of 38km that will study the star formation history of the universe. It will float west at nearly constant latitude for about 5 days before the flight is terminated over northwest Canada or northern Alaska. Real time position and flight track is available from the NSBF. Two of the graduate students working on the project have photo blogs of the entire (8 week) prep period, including several launch photos. The press has more traditional coverage as well. And if that isn't geeky enough to make it on Slashdot, the flight computers run Slack."

Re:Duration - Why Not Longer?

[prof_bart]

> Why not let the thing just float there forever?

The U.S. State Dept couldn't get overflight permissions from Russia (diplomatic issues).

> What is the primary failure mode? Loss of lifting gas?

Yes. For healthy (non leaking) balloons, this is primarily due to diurnal cycles. These are 0 pressure balloons. The gas expands and heats, and vents (to maintain 0 pressure) in the sun, but then cools contracts at night, so to avoid this, long duration flights are done above or below the arctic circle. The longest flights have been ~1 month (over Antarctica) and were terminated (Still flying well) because the McMurdo station summer season was closing.

> Is battery power an issue and is the payload powered by solar cells?

Yes (6 hrs on 4x12vx85Ah NiMH batteries) and Yes.

> What kind of ambient buffetting ocurrs at float altitude? Is there any percieved motion?

The outer frame of the gondola moves around by ~0.1 degree, with important resonances at 0.5 Hz and 0.05 Hz. The inner frame is stabilized to

> Is it difficult to create a parachute and floatation system to sheild the payload in various failure modes?

BLAST comes down on a 'standard' ~140' parachute. Take a look at Don or Gaelan's web pages linked off the story for launch pictures where you can see it. If it lands in a lake, we are very sad. If it lands in the Ocean, we are even more sad. NASA/NSBF decides when to release the gondola, so that neither will happen.

> What percent of the cost of the mission is the balloon, and what is the payload?

~20% Balloon + launch campaign costs/80% instrument and development for Long Duration experiments.

> What kind device or systems keep the orientation correct?

For Elevation: the inner frame is balanced and controlled with a torque motor.

For Azimuth, on short time scales ( > Can someone contact them? You just did.

Re:Duration - Why Not Longer?

[gmarsden]

It looks like prof_bart was about to answer these questions but got cut off.

> What kind device or systems keep the orientation correct? Gyroscopes?

We measure the pointing with gyroscopes for short time scales and star cameras to correct them on longer time scales, along with several other coarse sensors. We use 2 redundant sets of 3 orthogonal 1-d optical gyroscopes and 2 redundant 1-Mpix cameras behind 200 f/2 Nikon lenses. We expect to measure our pointing to less than 5 arcsec.

> If there are gyroscopes, are they a major percent of payload weight?

The two sets together weigh about 5 lbs, so less than 0.1% of the total weight.

We control the azimuth pointing with a 5-ft diameter reaction wheel, made of light-weight aluminum honeycomb with ~100 lbs of brass weights at the perimeter. The moment of inertia of the wheel is approximately 1% of that of the entire gondola. We keep the reaction wheel spinning at reasonable rates (~ 10 rpm) with a torque motor in the pivot. Elevation pointing is accomplished with a torque motor and a fluid balancing system to offset the cryogen boil-off.

We are always happy to answer questions, so ask away.

Re:Duration - Why Not Longer?

[Xandu]

* Didn't see an answer about which lifting gas - H2 or He?

I think that Prof. Barth's text got cut off in a weird way. He's probably tired. We all are. The balloon is filled with helium.

* Wouldn't launching from the North Pole station in summer (now, really) mean no daily temperature cycles or sunlight-heating differentials?

Which North Pole station are you talking about? The secret one that no one knows about? Seriously, the problem would be transportation. How would you get the (heavy) equipment out there? Where would we land when it's time to terminate the flight? We'd like to be able to recover the entire experiment, and there is basically no plane that could, in once piece, carry a 2700kg gondola from the polar ice cap back to civilization.

There are usually 2 balloon flights a year from McMurdo. People have talked about launches from South Pole (where there is a station), but the cost of getting everything out there is way way way to expensive, when McMurdo is almost as good (or better).

* Does anyone from Russia's version of the National Science Foundation or any of the Russian science bureaus read Slashdot?

Good question. Since it didn't make the front page, only the Science page, probably not. ;-)

* Was there something specific that caused Russia to say no to overflight rights?

Nothing specific, they currently prohibit everyone but the French. It's being worked on, but it's too late for us. Next season (next year) other experiments will probably be allowed to fly all the way around.

* Politics aside, what was the maximum probable mission time - just another day or two or (if going over Russia was possible) doubling to 14 or more days?

For an LDB balloon the nominal time is 14 days, and there have been flights as long as about 30 days. Those all flew from McMurdo (Antartica), where there is no issue with flying over other countries. (14 days happens to be about the time is usually takes to circumnavigate the pole at these altitudes).

For BLAST, we're limited by the cryogens in the cryostat that houses our detectors. As configured, we get about 11 days hold time. That would double our data time time around (looks like we'll get about 5 days at float). With a few modifications, we should be able to get the hold time to 14-15 days.

* Has anyone assigned probabilities to each of the various failure modes?

Historical data indicates that a balloon operates to achieve scientific minimums 95% of the time.
prof_barth tells me that annecdotally, about 1/5 experiments get torched on landing.

* If gondola weight determines spare gas capacity determines flying time, isn't there a way to just create an elastic balloon material that doesn't need a relief valve?

Theoretically, yes. They've tried, and NASA calls it ULDB (we're LDB, that's for long duration balloon, ULDB is ultra-long duration balloon). They've only just started to test them in the last few years, and so far they have all had some kind of failure (often a 'catastophic leak'). If they get one up that doesn't leak, they expect it'll last for 90 days or so. prof_barth says apparently, back in the early 90's, some small super-pressure balloons (w/ very small payloads) managed to go over 100 days.

And our balloon doesn't have a relief valve per se, it just has vents to the bottom that are open always.

* Are the bureacrats Russian or American or someone else? (Somehow I'm confident it's not the Canadians...)

Good question. both

* If politics determines mission time regardless of the technical stuff, WHO IS WORKING ON THE POLITICS? (I know, international relations can be much more complicated than the science, but its frustrating to hear from my side, too. I like to read about the cool stuff you're doing). Who do we contact to help push this along for the next mission?

I don't know. But the