Why Curiosity is a big deal

7 08 2012

With all the great press coverage of Curiosity, Cosmoboy’s family asked one unexpected question: “Why is there so much fuss about Curiosity when there have been a bunch of other Mars rovers?”

Although the “Countdown to Curiosity” articles detailed all of Curiosity’s amazing scientific apparatus, the articles didn’t really put into perspective how much better Curiosity is than the other Mars rovers (Sojourner, Spirit and Opportunity). So let’s right that wrong!

Sojourner landed way back in December 1996! I was actually studying for my PhD at the time, but there was a lot of great press coverage. It was perhaps the first space mission to really use the internet effectively. But for all the communication successes, Sojourner didn’t really have a great suite of scientific instruments. Given it’s small size, just a little over 10 kg and only 60 cm long, there wasn’t all that much space for scientific payloads. The key scientific instrument (other than cameras) was an Alpha Particle X-ray Spectrometer for determining the elements in rocks (Curiosity has a much more advanced one). But what many people remember about Sojourner was how slow it moved: it had a top speed of a little over 0.5 cm a second! But there again, this mission was put together on one tenth the budget of Curiosity.

The twin Spirit and Opportunity rovers came next, landing in January 2004. Like Sojourner, they both carried an APXS, but this time they came with more sophisticated spectrometers to make even better assessments of the precise elemental components of the Martian rocks and minerals. Much larger in size, at 185 kg and around 1.6 metres long, they were much more capable of carrying a heavy payload. They also had the advantage of a robotic arm so they could get in close and even abraid the surface of rocks to see what was lying underneath (the RAT tool!) But perhaps what everyone remembers about Spirit and Opportunity was their “Energizer Bunny” impressions – they just kept going and going! With it’s solar cells still operational, Opportunity is still working today after having covered almost 22 miles! Spirit got stuck in a dusty soil area in 2009 and unfortunately sent its last communication on 2010.

Fast forward to today’s super-rover: Curiosity! Now we’re talking about a 900 kg vehicle roaming about, which is capable of carrying half the total mass of Spirit in scientific experiments alone! NASA likes to use the analogy that Curiosity is about the same size as a Mini-Cooper. In terms of the scientific experiments, the list is pretty amazing (Curiosity is the first rover with a laser): ChemCam (remote sensing, including the laser, for chemistry) APXS, ChemMin (for mineraology and chemistry), SAM (detailed sample analysis), RAD (radiation assessment),  DAN (for detecting ice near the surface), REMS (for monitoring Martian weather) and not to mention a whole bunch of cameras! All in all, Curiosity is leaps ahead of went before it! It should truly help us understand the Martian geology and mineralogy in unprecedented detail.

Hopefully, that makes it clear why Curiosity is so important for studying Mars. It’s scientific designation, “Mars Science Laboratory” puts into perspective what this mission represents – a true suite of lab experiments on the surface of Mars!

And one last image to leave you with – a shot of all three rovers compared (but not on Mars!)


Tracking Curiosity

28 11 2011

Just a very quick post today, and one that’s a tad frustrated… I’ve been searching on line for a website that shows how far Curiosity is from Mars. If you go to the JPL mission website it will tell you how many days (great!) but I’m looking for something that tells you the distance. And so far I’ve found nothing… De nada. So I’d appreciate hearing from anyone who’s seen something like this on line.

In principle this isn’t too hard to do. You really only need a computer program that calculates the orbital trajectories of the Earth, Mars and Curiosity. Working out the distance from this model is actually easy. To set the model up you need the orbital positions and speed of all three of them. The Earth and Mars can be found easily, Curiosity seems a tad harder. I’m guessing it must be on line somewhere?

What you can find online is Curiosity’s position on the sky as it heads to Mars. JPL has it’s incredibly useful solar system data accessible through the HORIZONS on-line system. While I’ve not been able to figure out (yet!) how to get it to give me the orbital data I want, I have been able to use it to plot Curiosity’s celestial coordinates for the next month (these are for Halifax, Nova Scotia). While I’m not suggesting anyone go out and look, here are the next 6 days for fun:

Date__(UT)__HR:MN R.A._(ICRF/J2000.0) DEC

2011-Nov-28 00:00 08 19 14.59 -00 25 54.0

2011-Nov-29 00:00 m 08 21 53.08 +00 24 00.4

2011-Nov-30 00:00 m 08 22 59.29 +00 46 26.5

2011-Dec-01 00:00 m 08 23 33.30 +00 59 40.4

2011-Dec-02 00:00 m 08 23 51.82 +01 08 43.7

2011-Dec-03 00:00 m 08 24 01.34 +01 15 34.3

This area on the sky is between the constellations Hydra, Monoceros and Canis Major. Utah amateur astronomer Patrick Wiggins took this series of images on the morning of November 27th one day after launch (you can see Curiosity moves from frame to frame in the middle of the image)

As an added bonus HORIZONS will also tell you some additional data about Curiosity:

* Spacecraft
Mass: 3,893 kilograms total at launch,
2,401-kilogram EDL system (aeroshell + fueled descent stage)
539-kilogram fueled cruise stage

Cruise vehicle (cruise stage, aeroshell, w/rover & descent stage)
Diameter: 14 feet, 9 inches (4.5 meters)
height: 9 feet, 8 inches (3 meters)

Rover name: Curiosity
Rover dimensions:
Length: 9 feet, 10 inches (3.0 meters) (not counting arm)
Width: 9 feet, 1 inch (2.8 meters)
Height at top of mast: 7 feet (2.1 meters)
Arm length: 7 feet (2.1 meters)
Wheel diameter: 20 inches (0.5 meter)
Mass : 899-kilogram rover
Power: radioisotope thermoelectric generator & lithium-ion batteries

OK, so I’m sure I can probably hunt through the data from HORIZONS to figure out the trajectory, and then figure this all out! I’m sure, however, that the trajectory file is probably accessible somewhere, as it’s quoted in the data from HORIZONS as “msl_spk_cruise_1126-1502-tzero_v1_dsnsch”. It’s out there… Somewhere… Time to do some digging…

Curiosity Rover: Cruising on the Deep Space Network

27 11 2011

After all the excitement of yesterday’s launch, things are going to be fairly quiet until August. But Cosmoboy thought it would be fun to take a little look at Curiosity’s trip to Mars. How far does it have to go? How is the steering accomplished? How do we stay in contact?

Communicating with spacecraft is not easy. As the recent Phobos-Grunt disaster shows, once you lose contact getting it back is tough. The Earth’s rotation also means you can’t just rely upon one communication facility as every few hours it’s going to be pointing in the wrong direction. So you need a bunch of dishes dotted around the world. And that’s exactly what NASA’s Deep Space Network is, a system of three stations separated by 360/3=120 degrees apart on the Earth. There are dishes in:

Goldstone, in the Mohave Desert in California. The Goldstone facility actually contains five antennas, the biggest of which is the recently refurbished 70m “Mars” antenna. The name of this antenna actually comes from the face that it was first used to pick up the Mariner 4 spacecraft which had been lost by smaller antennas during its Mars fly-by. Since that time the dish has tracked Voyager 2 as it passed Uranus and Neptune as well as Spirit and Opportunity on Mars.

Robledo de Chavela, Spain which is about 60 km west of Madrid. (Note, the website is in Spanish, so unfortunately I couldn’t delve into as much detail as I hoped, and ironically it looks much better than the Goldstone website!).  This facility also has five antennas, including a 70m dish that weighs 8000 tons. Like the other two facilities, the receivers sit in an area that is somewhat bowl  shaped to shield it (as much as possible) from terrestrial radio interference.

Tidbinbilla, Australia which is about 30 km from Canberra (love the cows, this is farm land!). This station has the smallest number of active antennas, at three. Like the other two it’s largest dish is also 70m. Some film buffs probably remember the movie “The Dish” with Sam Neil, actually this facility isn’t the one referenced there. That was Honeysuckle Creek, which closed in 1981. In fact, there were once seven tracking stations across Australia.

Steering Curiosity is a bit like driving using your rear view mirror. The spacecraft relays signals back to the Earth and then course adjustments are sent back. Curiosity isn’t really looking for Mars or piloting toward it directly, instead that’s being handled through the DSN. Importantly, it has to be done with great accuracy, believe it or not sunlight will “push” Curiosity during it’s flight to Mars, and this needs to be taken into account (you don’t want to wind up hundreds of km off course). What’s more, by the time Curiosity reaches Mars and enters the atmosphere it needs to know very precisely where it is, any errors in position could be disasterous.  There’s only 70 kg of propellant to make course corrections, i.e. two tanks of gas in a 350 million mile journey!

Depending upon the precise launch time, NASA had a bunch of different possible trajectories all laid out. As it happens, Curiosity launched bang on the number one launch time of 10:02 am EST. With the trajectory laid out, it’s now a matter of tracking and making sure all the thruster burns happen on time. If you’re wondering, the thrusters are actually pretty low power, they have only 1 lb of thrust. Some of the maneuvers thus take hours of burn.

But by and large, getting Curiosity to Mars is routine. It’s been done before. And as I keep reminding everyone, the landing is where things get interesting!

Curiosity Launch: It went like clockwork!

26 11 2011

Congratulations to everyone involved with the Mars Science Laboratory launch!


Curiosity launched today at 10:02 am (Update: according to a NASA Kennedy tweet the official liftoff time was 10:02:00.211 a.m. EST – how’s that for precision!?) on a partly cloudy but otherwise good day at the Cape. The weather threatened to put things off early in the day with a little bit more rain than expected in the area, but otherwise things seemed to go really well. It was actually pretty funny to hear a NASA weather forecast that mentioned the incoming cosmic ray flux: “The proton flux is within bounds”. You don’t hear that on CBC! 🙂

Omar Baez, the NASA Launch Manager, commented

“…All the right things that they wanted to do in those crucial few minutes happened like clockwork.”

“The Atlas and Centaur were flawless. They got us to where the satelite needed to go we hit the window right at the beginning and everything appears nominal for the flight.”

During the countdown they focused closely on the wind and some of the rain bearing clouds in the area, but there was nothing of note to report other than a small couple of telemetry issues.

The interplanetary injection burn, and separation of the Curiosity spacecraft from the Centaur rocket all seemed to go perfectly from the vantage point of the onboard camera on the rocket (you could see the happy faces in the control room!) Can’t find a video of this on line yet… Update! Here it is. The spacecraft was picked up by the Deep Space Network just minutes later.

You can see the whole launch sequence here – it was just a perfect lift-off on a great day for flying!

Relief! (If I feel that way, I can’t begin to feel how good all the scientists and engineers that have worked for years on this project must feel!) Now we wait 8 months for Curiosity to make it’s way to Mars. Inertia and gravity are in control of the spacecraft now. But… when it gets close to Mars, things get really interesting

Countdown to Curiosity: 1 day to go!!!

25 11 2011

Weather update: it continues to look good for a launch tomorrow morning. The chance of rain is now down to 10%.


This is the final post in the “Countdown” series. Tomorrow Curiosity will begin its long journey to Mars. While the launch is a nerve wracking time for anyone involved, perhaps the most scary part of the mission is the landing. Curiosity will attempt to land on Mars using a method that’s never been used before: lowering down to the surface using a crane from a platform that is hovering under rocket power. If that sounds like it’s difficult to do – it is! NASA has a really neat movie of how it is all supposed to work.

Let’s quickly talk about the landing site first. Many of you will recall that during the Apollo missions the lunar module was piloted down to the surface. Neil Armstrong was actually seconds away from running out of fuel while he looked for a good place to put down Apollo 11, imagine what a disaster that could have been… Without the benefit of a human pilot, Curiosity needs to land in a region that’s relatively free of hazards. Fortunately, a series of surveyor satellites has given us incredible knowledge of the surface of Mars and the chosen site of Gale Crater has both good landing areas as well as a lot of interesting geography (including an alluvial fan likely deposited by water carrying sediments).

But let’s get back to the interesting bit, the landing procedure itself. Imagine hurtling toward a planet at tens of thousands of kilometers an hour. Your millions of miles away from the Earth and there’s no human pilot to plot a course once you’re inside the atmosphere to avoid any unexpected events. Sounds pretty risky, yeah? And it is… Beagle 2 was the last surface mission to fail (and we think we found the wreckage), but just four years earlier two missions, Mars Climate Orbiter and Mars Polar Lander, both failed as well. If you want statistics, NASA has landed on Mars successfully five (yes only five) times! And when it comes to Curiosity, the landing procedure that’s been chosen is more complex than any other mission before it…

While the Apollo missions entered into orbit around the Moon, Curiosity is going to slow down from interplanetary speeds without this step. In this sense its landing will be somewhat similar to the Apollo “splashdowns” on Earth. Thus Curiosity is going to hit the Martian atmosphere travelling at over 20,000 km per hour, and again, just like the Apollo missions, the spacecraft carrying Curiosity has a heat shield underneath to protect the rover from the extreme heat (a peak of 2100 C) produced in re-entry. All the steps that follow are given on this great graphic provided by NASA:

Once into the atmosphere Curiosity will begin a series of maneuvers at several times the speed of sound, before deploying its parachute while still at supersonic speeds. This part of the descent is anticipated to go pretty well. Supersonic breaking parachutes have been used since the Mercury missions in late 1950s early 1960s so the technology is nothing new.

But once Curiosity has descended to about 1.8 km above the surface, and is travelling at aroud 400 km per hour, it will separate from the parachute and begin a powered descent. In about 40 seconds it will be down to just 20m above the Mars surface, and then perhaps the most risky part of the whole mission begins: lowering to the surface on the end of a “sky crane”. Curiosity can’t just be “dropped” – it’s too heavy at almost 1 ton in mass. Once the sky crane is fully deployed the spacecraft will slowly descend down at about 0.75m per second. Once it detects that Curiosity is on the ground it will cut the lines on the crane and fly away at least 150 m away from the rover.

Amazingly, all this is going to be filmed. The MARDI descent camera will take 4 images per second during the maneuvers. If it all works, this is going to be one heck of a movie!

So, one day to go for the launch… Can’t wait for Curiosity to begin its journey!!!

Countdown to Curiosity: 2 days to go

24 11 2011

Weather update: Forecast for Cape Canaveral is still looking good for Saturday. There is a cold front that might possibly cause some problems, but forecasters put the probability of good launch weather still up around 70%


Yesterday we talked about the weather measurement experiments on Curiosity: the REMS package. Today we’ll focus an experiment that is going to measure the water and mineral content of Mars just below the surface. The name of the instrument is DAN, for Dynamic Albedo of Neutrons. The name may sound complicated, but the science behind the instrument is actually a simple idea.

DAN works in a quite ingenious way. If you fire high energy neutrons at a material then those neutrons will interact with the atomic nuclei in the material and either be absorbed or scattered in a certain direction. As it turns out, materials containing lots of hydrogen (which is typically locked up in either water or minerals) will slow down these high energy neutrons very efficiently and as a result the neutrons that are scattered will tend to be much lower energy than from regions with less hydrogen. That’s the basis of the experiment: fire neutrons at the ground and see what type of neutrons come back to your detector. If you get lots of low energy neutrons it means there’s a lot of water and minerals down there.

Life is always complicated though. So the big problem for Curiosity is that Mars is actually being bombarded constantly by cosmic rays which can create fast moving neutrons in the Martian surface. So any experiment you do has to be able to filter this effect out. DAN will actually do that using two detectors, one of which will block the low energy neutrons while the other will measure all the neutrons (including those generated by the cosmic rays). Subtract the two signals and you get the amount of low energy neutrons that are coming back.

How will DAN actually create the neutrons it fires into the ground? It will do so using a nuclear reaction of two types of hydrogen isotopes (tritium and deuterium) that will produce a helium nucleus plus a neutron as a result. This fusion reaction (deuterium is fired at a source containing tritium) will be very precisely controlled to produce a short pulse of neutrons that lasts about one millionth of a second. Once the neutrons have been fired then DAN switches over to follow the returning neutrons using its detectors. It will take data from 1 microsecond after the pulse through to about 10 milliseconds later.

But the neat thing about using a pulse is that you can figure out the distribution of water below the surface. The basic idea is you know exactly when the neutrons were fired and when the scattered neutrons were detected. Depending upon the depth of the water/mineral concentration the scattered neutrons will show up either earlier or later and in different amounts. From this time dependent signal we’ll be able to figure out just how deep the water is (at least down to about ~0.5m, the limit of what DAN can probe).

DAN’s overall role in MSL is pretty important. It’s going to provide a very clear picture of the overall water/mineral content just below the surface wherever Curiosity goes. It’s got over 10 million shots stored, so there isn’t too much worry about it being “used up” too quickly. It can also be used during traverses as well, there’s no need to stop and take a measurement. And on top of figuring out the subsurface water, DAN can also be used to look at the overall flux of neutron radiation background in the Mars environment. It’s a pretty neat little instrument.

Tomorrow: The impressive but risky descent

Countdown to Curiosity: 3 days to go

23 11 2011

While yesterday we focused on radiation measurements on Mars, and the RAD experiment, today we’ll look how Curiosity is going to measure the Martian atmospheric conditions, or Martian weather if you want to think about it that way. The instrument(s) that will make these measurements form the Rover Environmental Monitoring Stations (REMS).

The Martian atmosphere is both very thin and much lower pressure than the Earths (the average pressue is about 150 times lower than at sea level on Earth). The elemental composition is very different too, Mars’ atmosphere is dominated by carbon dioxide (95%) and there is only a tiny fraction of oxygen (0.1%). Combined with a variation of surface temperature from -87 C through to (very localized) highs of 30 C in the southern regions (although mean surface temps are around -60 C), Mars is expected to have some quite unique planetary weather.

For our weather forecasts on Earth we like to know temperature, wind speed, humidity, atmospheric pressure and some times the UV levels. So it will come as no surprise that’s pretty much what Curiosity is going to measure. In fact, Curiosity will measure the following six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and ultraviolet radiation.

Anyone who has worked at a weather station knows that you need to put sensors measuring wind speed (for example) slightly above the ground to get away from surface effects. The two wind speed sensors thus sit on Curiosity’s Remote Sensing Mast (on two separate booms, one pointing forward and another at 120 degrees to the first), along with humidty and air & ground temperature sensors. Placing the booms at different angles ensures that at least one of them will record accurate wind data for any given wind direction. Note, even on the mast the wind measurements will still be slightly impacted by air flow around the mast itself. The wind speed measurements will be pretty accurate, with a resolution of around 0.5 m/s. The directional measurements are anticipated to be accurate to within 30 degrees or so, and it will even measure vertical variation in wind direction to within 10 degrees.

Even though the ground temperature sensor is up on the mast, it can still measure the temperature of the ground by pointing toward a patch to the side of the rover. The temperature sensor is an electrical one, a thermopile, and can record in a temperature range of 150-300K with an accuracy of around 10K. The air temperature measurements made on the boom itself will be twice as accurate (to within 5K) over the same temperature range. The pressure and humidity sensors complete the instrument suite on the mast.

Since the UV sensor is designed to measure the incoming UV from above the rover, it sits on top of the rover deck to the back. Much like the radiation assessment detector (RAD) the UV sensors are sensitive to incoming radiation across about a 60 degree cone above the rover. The sensor itself will be able to detect UV in six different wavelength ranges, (from UVA through to UVE, plus a “total dose” across the entire range) and will thus characterize the UV environment in great detail.

But really the great “value add” behind all these measurements is that Curiosity will make them systematically every hour. So for each hour of each Martian day, Curiosity will record 5 minutes of data from all the sensors. To do this REMS has been set up to work independently of the main power sources on Curiosity and can take data even when the rover is in a sleep mode.

From all this data we’ll be able to develop detailed models of Martian weather patterns, with a detailed focus both on large scale fronts and smaller, so called microscale weather systems. The microscale systems include small whirlwinds like dust devils. We’ll also uncover precisely how the Martian water cycle works, and it’s going to be seriously different from the Earth’s!

And to whet your appetite for all this new Martain weather data, here’s a beautiful Martian sunset taken by the Spirit Rover. Tomorrow: DAN.