Thursday, June 28, 2012

Luna 15 and Apollo 11: A Near-Miss on the Moon?

It was mid-day on July 21, 1969. Engineers at Mission Control in Houston were preparing for Apollo 11's departure from the moon. Neil Armstrong and Buzz Aldrin's excursion onto the moon's surface was over, and they were stowing equipment in preparation for liftoff early in the afternoon. Meanwhile, a Soviet probe, Luna 15, crash landed on the moon!

Apollo 11. Source: Wikipedia.

Luna 15 was launched three days before the Apollo 11 lift-off. Its aim was to land on the lunar surface, collect rock samples, and return to Earth. If all went well, it could have arrived back on Earth the same day the astronauts came home: a small victory for the Soviets (whose Luna 2 spacecraft was the first human-made object to reach the moon, in 1959). But after several dozen orbits of the moon, the probe's landing didn't go as planned. It stopped transmitting four minutes into its descent, and crashed at Mare Crisium.

A Luna probe. Source: Wikipedia.

I was curious about how far the Luna crash was from the Apollo 11 Lunar Module. Mare Crisium is the "sea" directly north of Mare Tranquilltatis, site of Apollo 11's landing. According to Yahoo Answers (maybe not the most reliable source?), the two crafts were a little over 740 miles apart. 

Was the Apollo 11 mission ever in danger of a collision with Luna 15? Were the Soviets aiming to crash their probe into the Lunar Module? We know now that the answer to both questions was "no." But apparently back in 1969 NASA officials had some concerns. Astronaut Frank Borman put a call into one of the leaders of the Soviet space program, Dr. Mstislav Keldysh, asking him to confirm that the probe posed no threat to Apollo 11's mission. In what some describe as the very first instance of U.S.-Soviet cooperation in the space race, the Soviets released Luna 15's flight plan to NASA officials, allaying fears that it was on a collision course with the Lunar Module or the Command Module. 

During their mission, Armstrong, Aldrin, and Michael Collins were kept apprised of Luna 15's status. Apparently there were others tracking the craft as well. Astronomers at the University of Manchester Jodrell Bank radio telescope eavesdropped on Luna 15's final minutes. Their recordings were released in 2009; you can listen to a British scientist narrate the craft's crash here.

Jodrell Bank Observatory. Source: Space Today.

So the space race effectively ended that day. Americans were first to walk on the moon, hours before an unmanned Soviet landing failed. But, in the process, the U.S. and the U.S.S.R. first cooperated in space!

Sources: Yahoo Answers (always reliable???); Wired; NASA; Collect Space

Monday, June 25, 2012

What time is it on Mars?

As of when I'm writing this post, it's 5:01 Mars Solar Time on the edge of the Endeavor Crater on Mars. That's where the Opportunity Rover is sittingFor comparison, right at this moment, where I am on Earth, the time is 9:24 PM CDT. 

Mars Time! Source: NASA
(You can download this clock too, from NASA.)

Since Mars spins at a different rate than Earth, Martian days are not 24 hours long. A Mars day is 24 hours, 39 minutes, and about 35 seconds long. So, not too far off from an Earth day... and really not a problem at all, since there isn't anybody living on Mars, right? Wait, but what about all those people who are living on Earth but working on Mars? As in, the team of Jet Propulsion Laboratory scientists and engineers who support Mars missions ... what about them?

Late afternoon, Mars Time: Opportunity's shadow across Endeavor Crater. Source: NASA

The Mars Exploration Rover mission, featuring the Spirit and Opportunity rovers, landed in 2004. The first 90 days of that mission were the most intense, with the two solar-powered rovers working during the day and sleeping at night. At the end of every Mars Day, data from the rovers' activities was uploaded via satellite and sent to Earth. And then, while the rovers sleep, the humans needed to work: analyzing the data and planning for the next Martian sol (day). 

So, for those first 90 days, folks working on the mission lived on Mars Time! Adding an extra 39 minutes to each day means that while you may begin the week on Monday reporting to work at 9:00 AM PST, by the following Monday you are reporting to work around 1:30 PM PST, and so on. As one might imagine, it is a grueling schedule. A team member, asked for suggestions in adhering to Mars Time, recommended staffing the next Mars mission with "childless, unmarried orphans."

Since Earth restaurants operate on Earth Time, mission staff at JPL relied on late-night (Earth Time) catering to ensure they could get lunch every Martian Day. Snacks available on site included ice cream... according to a NASA report, it was pretty typical for staff to eat 3-5 ice cream bars every Martian day: "Some people gained weight. There is anecdotal evidence that team members relied on the ice cream as both a reward and a pick-me-up to push through the harder parts of their shift work." 

Source: Mars Ice Cream's Facebook Page.

My first three blog posts left me really wanting to travel into outer space. This blog post is making me hungry. And making me want to travel to the Ice Cream Capital of the World.

Another aspect of Mars Time was that clocks at JPL were set to dual displays, for the local timezone on both planets. In his excellent book about the Mars Exploration Rover mission, Principal Investigator Dr. Steve Squyres explains how he and other mission personnel had watches made specially for Mars Time.

A Mars Time watch face. Source: NASA.

For the Mars Exploration Rover mission, Mars Time shifts ended 90 days into the mission. After that, folks synced their work schedules with Mars night time to a certain extent, but no longer punched the Martian time clock. 

Source: Mars Ice Cream Co.; NASA; NPR; Deborah Bass, Choosing Mars Time: Analysis of the Mars Exploration Rover Experience

Thursday, June 21, 2012

Why didn't Apollo 10 land on the moon?

Apollo 10 was humanity's second trip to the moon, and the first to include a lunar module (nicknamed "Snoopy"). A main mission objective was to test out the lunar module in advance of Apollo 11's historic landing. This included undocking the lunar module from the command module, and then flying it down from lunar orbit to just over 8 nautical miles above the moon. That's so close to landing! At that altitude, the lunar module was closer to the moon than a commercial airliner on a transatlantic flight is to Earth.

Eastern Siberia. The view from a Boeing 777 en route to Chicago from Beijing.

Which has lead me to wonder: why didn't Apollo 10 Commander Tom Stafford and Lunar Module Pilot Gene Cernan just fly those 8 extra miles, touch down, get out and walk around on the moon, and then fly back? Either in a rogue Space Cowboys style maneuver, or as part of an official plan to hustle along the Apollo program, moving up the landing from July 1969 to May 1969?

It was, after all, a space race! 

Space race! Source: haro-online.

Cernan himself said that Snoopy didn't have enough fuel to fly to the moon, land, and then take off again to dock with the command module:

"A lot of people thought about the kind of people we were: 'Don't give those guys an opportunity to land, 'cause they might! So the ascent module, the part we lifted off the lunar surface with, was short-fueled. The fuel tanks weren't full. So had we literally tried to land on the moon, we couldn't have gotten off."

Apparently this is a bit of an exaggeration. Snoopy might have actually had enough fuel to land and return to orbit. Since the mission was a dress rehearsal for Apollo 11, it was a close approximation of that mission, down to details such as the weight of the fuel in the lunar module. Snoopy weighed in at 30,375 pounds; the Apollo 11 lunar module was only about 2,500 pounds heavier. But, Snoopy didn't have enough fuel to get to the surface and back safely, meaning, with a reasonable margin for error. And beyond that, the lunar module had only flown in space one time before, and never in lunar orbit. The craft was still undergoing final testing in preparation for the Apollo 11 landing.

Apollo 10 lunar module, not going rogue. Source: Discovery News.

If Stafford and Cernan had been the first to land on the moon, the Apollo 10 lunar module itself probably wouldn't have survived long. Following each successful moon landing, the crew compartment of the lunar modules were jettisoned in lunar orbit, slowly deorbiting and crashing into the moon. 

Since Stafford and Cernan didn't land, Apollo 10's lunar module wasn't jettisoned until the mission was en route to Earth. So since the lunar module never made it to the moon, it's intact, and decades later, it's still orbiting the sun! There's even a group of astronomers trying to find it

Even though they never made it to the lunar surface, Tom Stafford (who never walked on the moon), Gene Cernan (who eventually did, during Apollo 17), and Snoopy set two big space records. The Apollo 10 mission has traveled faster than any other manned mission: 24,790 miles per hour (or .0037% the speed of light). Because the moon happened to be near the apogee of its orbit from Earth during the mission, it's also the furthest humans have ever traveled from home: 254,110 miles from Houston to the far side of the moon!

Monday, June 18, 2012

"Seven minutes of terror"

"Seven minutes of terror." That's how folks are describing the upcoming August 6 landing of Curiosity on Mars.

Terror on Mars. Source: NASA.

Terror on Mars. Source: Ghosts of Mars.

Historically, any Mars mission has run a pretty big risk of failing. It's the planet where space robots go to die. But Curiosity's mission is tricky for a new reason. The Curiosity rover is the biggest object anyone's tried to land on Mars. It weighs 1,984 pounds, or in more useful terms, the weight of nine baby elephants.

Cuddle me! Source: Wikipedia Commons.

That's the heaviest rover humans have ever attempted to land on Mars. While previous missions slowed on final descent with retrorockets on the craft and/or bounced to a final landing with airbags, that won't work for Curiosity.

Apollo 11 splashdown. Source: NASA.

A parachute will be deployed to initially slow Curiosity's landing, but that wouldn't be enough to slow the craft to a safe speed. Parachutes are enough on Earth, but the Martian atmosphere is much less dense than Earth's atmosphere. Instead, a mile from the ground, the spacecraft's cover will come off, and a "sky crane" will emerge, holding the rover below it, attached by tethers. The sky crane has retrorockets, which it will use to fly Curiosity to its landing site, and then drop the rover on the ground. Then, the sky crane tethers will detach and it will zoom off and crash at a safe distance. The rover will have been gently placed on the ground, wheels down, ready to roll.


The advantage of the sky crane system over airbags is size and weight: Curiosity can be much larger and heavier than previous mini-rovers that descended to Mars surrounded by airbags and then bounced to a landing. The advantage of the sky crane system over attached retrorockets is that an actual wheeled rover can land, and then drive around Mars without rockets attached (or without the trouble of detaching rockets from its underside after landing).

I'm not an engineer. This is how my non-engineer brain assesses the risk of the sky crane: it's better than airbags because we want to eventually land people on Mars, and we can't do that by bouncing their craft to the ground. And it's better to have the rover attached to the retrorockets with a tether that can be severed quite easily than attached to retrorockets by a more permanent, but complicated system that contains more parts that could break.

Fingers crossed for August 6!

Sources: Discovery News; NASA JPL; Scientific American.

Tuesday, June 12, 2012

What are the odds of safely travelling to Mars?

As of today, NASA's Curiosity Rover is less than 66 million miles from Mars. It's scheduled to land at Gale Crater on August 6. What are the odds that it will actually get there, in one piece?

Curiosity's destination, Aeolis Mons, inside Gale Crater. Source: Wikipedia.

If we count up every single human attempt to launch something at Mars, aimed at landing on the planet, orbiting it, or flying by, the answer is 47%.

But! That's not the full story. That 47% takes into account all probe launches between 1960 and today, and we have gotten a lot better at sending things to Mars in the last fifty years. How much better? Between 1960 and 2000, 41 missions were launched. Roughly 15 reached Mars orbit, landed, or completed a fly-by. So the success rate was less than 37%. Since 2000, we've launched 11 probes, not counting Curiosity. So far 8 have succeeded- a 73% success rate!

What else might affect Curiosity's chances? It doesn't hurt that its a NASA mission... out of 20 NASA Mars missions, 14 succeeded- so 70% odds. Way better than Russia's success rate over the past fifty years. Though I don't want to slam the Russians. The Soyuz is fantastic, and if you're a person rather than an unmanned lander it's the only into outer space right now...

One final consideration. It's easier to make it into Mars orbit than to land on Mars. Humans have attempted 17 unmanned landings on Mars (and one on Phobos). About 7 succeeded- 41%. And Curiosity's landing will be particularly challenging. More on that in my next post...

Mars Science Laboratory's planned landing. Source: Wikipedia.

I'm nervous just thinking about August 6th. But at least we're trying, right? And for anyone keeping score- Earth is winning! Mars hasn't launched anything at us, besides meteorites.

Meteorites and this dude. Source: Wikipedia.