In 1943, JPL was under contract with the Army Air Corps to design, build and test an underwater solid rocket motor. Early tests were done in a large trough of water to see if a solid propellant would fire underwater ... and it did. Field tests were conducted in 1943 at the Morris Dam Test Facility in an artificial lake 25 miles from Pasadena, California. The facility was part of Caltech’s “other” rocket project, funded by the National Defense Research Committee of the Office of Scientific Research and Development – an agency set up to support and coordinate war-related research.
This photo shows a barge, which was anchored to trees on the shore of the lake, with an underwater structure that would hold the motor at a depth of one to six feet during testing. Two motion-picture cameras (one color, and one black and white) filmed the ten tests. The test motors were loaded with two different propellant formulas (GALCIT 53 and GALCIT 54).
JPL had a growing need for its own underwater test facility, so construction began on a hydrodynamic tank, or towing channel, in September 1943. It was located in the space currently occupied by the parking structure and part of Arroyo Road. An Army Air Forces contract for $121,000 – for development of a hydrobomb design – began in September 1944.
Dear Superintendawnts and Assisdawnts,
An intrepid interplanetary explorer is now powering its way down through the gravity field of a distant alien world. Soaring on a blue-green beam of high-velocity xenon ions, Dawn is making excellent progress as it spirals closer and closer to Ceres, the first dwarf planet discovered. Meanwhile, scientists are progressing and analyzing the tremendous volume of pictures and other data the probe has already sent to Earth.
Dawn is flying down to an average altitude of about 240 miles (385 kilometers), where it will conduct wide-ranging investigations with its suite of scientific instruments. The spacecraft will be even closer to the rocky, icy ground than the International Space Station is to Earth's surface. The pictures will be four times sharper than the best it has yet taken. The view is going to be fabulous!
Dawn will be so near the dwarf planet that its sensors will detect only a small fraction of the vast territory at a time. Mission planners have designed the complex itinerary so that every three weeks, Dawn will fly over most of the terrain while on the sunlit side. (The neutron spectrometer, gamma ray spectrometer and gravity measurements do not depend on illumination from the sun, but the camera, infrared mapping spectrometer and visible mapping spectrometer do.)
Obtaining the planned coverage of the exotic landscapes requires a delicate synchrony between Ceres' and Dawn's movements. Ceres rotates on its axis every nine hours and four minutes (one Cerean day). Dawn will revolve around it in a little less than five and a half hours, traveling from the north pole to the south pole over the hemisphere facing the sun and sailing northward over the hemisphere hidden in the darkness of night. Orbital velocity at this altitude is around 610 mph (980 kilometers per hour).
The planned altitude differs from the earlier, tentative value of 230 miles (375 kilometers) for several reasons. One is that the previous notion for the altitude was based on theoretical models of Ceres’ gravity field. Navigators measured the field quite accurately in the previous mapping orbit (using the method outlined here), and that has allowed them to refine the orbital parameters to choreograph Dawn’s celestial pas de deux with Ceres. In addition, prior to Dawn’s investigations, Ceres’ topography was a complete mystery. Hubble Space Telescope had shown the overall shape well enough to allow scientists to determine that Ceres qualifies as a dwarf planet, but the landforms were indiscernible and the range of relative elevations was simply unknown. Now that Dawn has mapped the topography, we can specify the spacecraft’s average height above the ground as it orbits. With continuing analyses of the thousands of stereo pictures taken in August – October and more measurements of the gravity field in the final orbit, we will further refine the average altitude. Finally, we round the altitude numbers to the nearest multiple of five (both for miles and kilometers), because, as we will discuss in a subsequent Dawn Journal, the actual orbit will vary in altitude by much more than that. (We described some of the the ups and dawns of the corresponding orbit at Vesta here. The variations at Ceres will not be as large, but the principles are the same.)
To attain its new orbit, Dawn relies on its trusty and uniquely efficient ion engine, which has already allowed the spacecraft to accomplish what no other has even attempted in the 58-year history of space exploration. This is the only mission ever to orbit two extraterrestrial destinations. The spaceship orbited the protoplanet Vesta for 14 months in 2011-2012, revealing myriad fascinating details of the second most massive object in the main asteroid belt between Mars and Jupiter, before its March 2015 arrival in orbit around the most massive. Ion propulsion enables Dawn to undertake a mission that would be impossible without it.
While the ion engine provides 10 times the efficiency of conventional spacecraft propulsion, the engine expends the merest whisper of xenon propellant, delivering a remarkably gentle thrust. As a result, Dawn achieves acceleration with patience, and that patience is rewarded with the capability to explore two of the last uncharted worlds in the inner solar system. This raises an obvious question: How cool is that? Fortunately, the answer is equally obvious: Incredibly cool!
The efficiency of the ion engine enables Dawn not only to orbit two destinations but also to maneuver extensively around each one, optimizing its orbits to reap the richest possible scientific return at Vesta and Ceres. The gentleness of the ion engine makes the maneuvers gradual and graceful. The spiral descents are an excellent illustration of that.
Dawn began its elegant downward coils on Oct. 23 upon concluding more than two months of intensive observations of Ceres from an altitude of 915 miles (1,470 kilometers). At that height, Ceres' gravitational hold was not as firm as it will be in Dawn's lower orbit, so orbital velocity was slower. Circling at 400 mph (645 kilometers per hour), it took 19 hours to complete one revolution around Ceres. It will take Dawn more than six weeks to travel from that orbit to its new one. (You can track its progress and continue to follow its activities once it reaches its final orbit with the frequent mission status updates.)
On Nov. 16, at an altitude of about 450 miles (720 kilometers), Dawn circled at the same rate that Ceres turned. Now the spacecraft is looping around its home even faster than the world beneath it turns.
When ion-thrusting ends on Dec. 7, navigators will measure and analyze the orbital parameters to establish how close they are to the targeted values and whether a final adjustment is needed to fit with the intricate observing strategy. Several phenomena contribute to small differences between the planned orbit and the actual orbit. (See here and here for two of our attempts to elucidate this topic.) Engineers have already thoroughly assessed the full range of credible possibilities using sophisticated mathematical methods. This is a complex and challenging process, but the experienced team is well prepared. In case Dawn needs to execute an additional maneuver to bring its orbital motion into closer alignment with the plan, the schedule includes a window for more ion-thrusting on Dec. 12-14 (concluding on Dawn's 3,000th day in space). In the parlance of spaceflight, this maneuver to adjust the orbit is a trajectory correction maneuver (TCM), and Dawn has experience with them.
The operations team takes advantage of every precious moment at Ceres they can, so while they are determining whether to perform the TCM and then developing the final flight plan to implement it, they will ensure the spacecraft continues to work productively. Dawn carries two identical cameras, a primary and a backup. Engineers occasionally operate the backup camera to verify that it remains healthy and ready to be put into service should the primary camera falter. On Dec. 10, the backup will execute a set of tests, and Dawn will transmit the results to Earth on Dec. 11. By then, the work on the TCM will be complete.
Although it is likely a TCM will be needed, if it turns out to be unnecessary, mission control has other plans for the spacecraft. In this final orbit, Dawn will resume using its reaction wheels to control its orientation. By electrically changing the speed at which these gyroscope-like devices rotate, the probe can control its orientation, stabilizing itself or turning. We have discussed their lamentable history on Dawn extensively, with two of the four having failed. Although such losses could have been ruinous, the flight team formulated and implemented very clever strategies to complete the mission without the wheels. Exceeding their own expectations in such a serious situation, Dawn is accomplishing even more observations at Ceres than had been planned when it was being built or when it embarked on its ambitious interplanetary journey in 2007.
Now the mission lifetime is limited by the small supply of conventional rocket propellant, expelled from reaction control system thrusters strategically located around the spacecraft. When that precious hydrazine is exhausted, the robot will no longer be able to point its solar arrays at the sun, its antenna at Earth, its sensors at Ceres or its ion engines in the direction needed to travel elsewhere, so the mission will conclude. The lower Dawn's orbital altitude, the faster it uses hydrazine, because it must rotate more quickly to keep its sensors pointed at the ground. In addition, it has to fight harder to resist Ceres' relentless gravitational tug on the very large solar arrays, creating an unwanted torque on the ship.
Among the innovative solutions to the reaction wheel problems was the development of a new method of orienting the spacecraft with a combination of only two wheels plus hydrazine. In the final orbit, this "hybrid control" will use hydrazine at only half the rate that would be needed without the wheels. Therefore, mission controllers have been preserving the units for this final phase of the expedition, devoting the limited remaining usable life to the time that they can provide the greatest benefit in saving hydrazine. (The accuracy with which Dawn can aim its sensors is essentially unaffected by which control mode is used, so hydrazine conservation is the dominant consideration in when to use the wheels.) Apart from a successful test of hybrid control two years ago and three subsequent periods of a few hours each for biannual operation to redistribute internal lubricants, the two operable wheels have been off since August 2012, when Dawn was climbing away from Vesta on its way out of orbit.
Controllers plan to reactivate the wheels on Dec. 15. However, in the unlikely case that the TCM is deemed unnecessary, they will power the wheels on on Dec. 11. The reaction wheels will remain in use for as long as both function correctly. If either one fails, which could happen immediately or might not happen before the hydrazine is depleted next year, it and the other will be powered off, and the mission will continue, relying exclusively on hydrazine control.
Dawn will measure the energies and numbers of neutrons and gamma rays emanating from Ceres as soon as it arrives in its new orbit. With a month or so of these measurements, scientists will be able to determine the abundances of some of the elements that compose the material near the surface. Engineers and scientists also will collect new data on the gravity field at this low altitude right away, so they eventually can build up a profile of the dwarf planet's interior structure. The other instruments (including the camera) have narrower fields of view and are more sensitive to small discrepancies in where they are aimed. It will take a few more days to incorporate the actual measured orbital parameters into the corresponding plans that controllers will radio to the spacecraft. Those observations are scheduled to begin on Dec. 18. But always squeezing as much as possible out of the mission, the flight team might actually begin some photography and infrared spectroscopy as early as Dec. 16.
Now closing in on its final orbit, the veteran space traveler soon will commence the last phase of its long and fruitful adventure, when it will provide the best views yet of Ceres. Known for more than two centuries as little more than a speck of light in the vast and beautiful expanse of the stars, the spacecraft has already transformed it into a richly detailed and fascinating world. Now Dawn is on the verge of revealing even more of Ceres' secrets, answering more questions and, as is the marvelous nature of science and exploration, raising new ones.
Dawn is 295 miles (470 kilometers) from Ceres. It is also 3.33 AU (309 million miles, or 498 million kilometers) from Earth, or 1,270 times as far as the moon and 3.37 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.
Dr. Marc D. Rayman
5:00 p.m. PST, November 30, 2015
The purpose of my deployment to Antarctica is to help the Stratospheric Terahertz Observatory II (STO-2) team launch a science payload to look at the star forming regions in the galaxy. STO-2 will fly aboard a Long Duration Balloon (LDB). The LDB program is part of the Columbia Scientific Balloon Facility, which launches payloads all over the world.
The STO-2 team traveled to the LDB headquarters in Palestine, Texas, last July and August for a hang test to ensure the payload is ready for launch. From there it was taken apart and shipped to Antarctica. The gondola was then shipped to New Zealand on a barge and flown from New Zealand to McMurdo Station on a supply mission. The instrument was flown the whole way to McMurdo.
The STO-2 team just after passing the hang test in Palestine, Texas, in August 2015. Image credit: Christopher Walker
After shipping the payload, the team started to reassemble it in the second half of October on the ice. (I was waiting to travel to McMurdo until backup parts were completed in mid November in case important equipment failed.) It's here in McMurdo that we unpack and reassemble the payload and continue instrument testing and reintegration.
Every day, we leave McMurdo at 7:30 a.m. and travel about six miles from McMurdo Station to the LDB facility just beyond Willy Field on the Ross Ice Shelf. We arrive between 8:05 and 8:15 depending on the driver and the mode of transportation. One of the buses is Ivan "the terra" bus, pictured below. The field camp consists of two hangars for the the payloads, a dining hall (called the galley), a bathroom facility and two smaller shelters for the Columbia Scientific Balloon Facility staff. This year, there are two payloads, STO-2 and the Gamma Ray Imager/ Polarimeter for Solar flares (GRIPS) payload. In some years there are three payloads, but never more than that.
The LDB facility. From the left: a yellow storage facility, the GRIPS hangar (green stripe), the STO-2 hangar (brown stripe), the CSBF machine shop, the CSBF telemetry workshop, the bathroom, and all the way to the right, the yellow tent is the galley. Image credit: Jenna Kloosterman
There's a cook in the galley during lunchtime and coffee, tea, and hot chocolate
whenever you need it. Furthermore, we have views of Mt. Erebus, the
southern-most active volcano on Earth. Most days it is covered in
clouds, but when the clouds clear, it's one of my favorite things to
photograph. For a harsh continent, it's a good life!
After a full day of work, we leave LDB at 5:30 p.m. and are back in McMurdo for dinner between 6:05 and 6:15 p.m.
Boarding Ivan "the terra" bus with my colleague Jose Siles. Image credit: Jose Siles
The STO-2 gondola team has successfully tested the pointing system for the telescope, pointing on the sun and Venus. In order to do their tests, they had to open the hangar doors so the hangar could cool to the ambient temperature -- about 20 degrees F right now. The instrument team is glad that they are done until integration of the instrument with the gondola is complete.
The STO-2 instrument will be explained for a general audience in a future post. For our colleagues following us back home, the team has made progress in aligning the 1.5 and 1.9 THz local oscillators and is simultaneously conducting beam pattern measurements. The 4.7 THz channel has measured a Y-Factor (sensitivity measurement). If you are interested in the details, please communicate with us privately.
Every year in the summer as the sea ice melts, it is pushed up against the permanent ice shelf due to tidal forces. When this happens, the pressure from this force cracks the ice into ridges near Scott Base. Last night, I was lucky enough to walk through the pressure ridges that are formed this way with a group from the Long Duration Balloon Facility. We saw beautiful ice formations, Weddell Seals (including one that had just given birth) and melt ponds. Please see the slideshow above for the new phrase I'm coining, "Make like a seal." Words cannot describe the scenery, so just enjoy the slideshow!
The instrument I came to Antarctica to work on, the Stratospheric Terahertz Observatory II (STO-2), in the most basic terms is designed to study how stars are born. Although I'll avoid getting too technical on most of my posts here, this entry will be on the more technical side to provide an update to my colleagues back at JPL and around the world.
STO-2 uses superconducting mixers, which requires cooling it to below 9 K (that's -443 degrees F). In order to achieve this temperature, we first "precool" our cryostat to 77 K (-321 degrees F) using liquid nitrogen, and then cool using liquid helium to 4 K (-452 degrees F). The whole process takes about 48 hours.
Today, we finished the helium fill. I participated in the fill, but you cannot see me in the picture above because I was behind the shelves on the left.
The transfer occurs from a 500 L liquid helium storage Dewar (yes, as in James Dewar, the scotch-maker -- he made whiskey to support his science habit) to the 100 L liquid helium tank on the STO-2 instrument on the right.
Although it takes about 24 hours after the fill is complete to cool everything inside the cryostat to 4 K, it was cold enough after an hour to confirm that we have five live mixers with superconducting currents! We also have five local oscillator channels working! There is still much work to be done, but overall this is a very positive sign that we are on our way to a successful mission!
I spent my first day on the ice at the Long Duration Balloon (LDB) Facility, where we work daily to prepare the STO-2 gondola and instrument. (LDB will be the subject of many future posts.)
After work, I attended a training session on outdoor skills in Antarctica. The training itself covers the flagging system (aka early GPS, so you know that you are on the trail and not walking into a snow covered crevasse) and procedures for checking out at the firehouse to let the right people know you are out hiking.
It is mostly common-sense, straight-forward information, but was required in order to walk down to the Ob Tube (Observation Tube), which I did with my friends and colleagues Chris and Kay from Arizona State University promptly after completing the training.
The Ob Tube is a hole is drilled in the sea ice and a long tube with an observation deck is inserted at the bottom. From here, one can observe the beauty of the sea. I saw only small fish and beautiful ice formations inside the Ob Tube, but a seal was resting on the sea ice outside. We also had a fantastic view of Ob Hill (Observation Hill). Enjoy the pictures from the evening!
The big day arrived! I set my alarm for 4:15 a.m. and I was out the door at 4:45 to take the shuttle to the United States Antarctic Program (USAP) Passenger Terminal. We put on most of our ECW at the CDC and wheeled all of our luggage into the terminal. We had to fill out a boarding card, and then your name is matched to the passenger manifest. Boarding passes are handed out with numbers. The flight crew weighs absolutely everything before it gets on the flight. Each passenger is allowed 85 lbs of personal luggage, although any ECW passengers are wearing is not counted against them. My luggage weighed in at 75 lbs -- I packed too light apparently (joking!).
Getting dressed in my ECW at the CDC before my ice flight. Image credit: Jenna Kloosterman
After checking in, we had a little time to eat a light breakfast and watch our last sunrise until we return to New Zealand. We watched a few more orientation videos and then went through a security screen. At the end of the security screen, we boarded a bus, which drove out to the tarmac to meet our plane. To my relief, it was a C-17!!! That means a plane with a jet engine, a five-hour flight time, a bathroom, and real seats. A first class military cargo plane!!! They hurried us on the plane, but I managed to hand my camera to a new friend to snap a quick picture as I boarded the plane.
Our flight last a little over five hours. The most concerning part was the "exit" sign on the ceiling! For the last two hours of the flight, we had sweeping views of the ice out the one window in the C-17.
First views of the sea ice shelf in Antarctica! Image credit: Jenna Kloosterman
We had a smooth landing at Pegasus Field. When the door to the C-17 was opened, a cold blast of Antarctic air filled the plane. Temperatures this time of year range in the 10-20 degree F range. I realized that I had left my sunglasses on one of my checked bags, so I put on my CDC-issued goggles. I snapped a quick picture of the C-17 and then boarded Ivan "the terra" bus. An hour drive to McMurdo Station and we were dropped off at the Chalet for more on-ice orientations. At the end, we were given our room assignments. We had to pick up bedding (sheets and blankets) from Building 155 across from the dorms and our luggage at Building 140. Fortunately, there was a shuttle-bus driver to help me carry my 75 lbs of luggage from Building 155 to my dorm in Building 208. All I had to do was haul it up three flights of stairs!
Last time I was in McMurdo, I was placed in a triple room in Building 203. Compared to that, Building 208 is the Hilton! All rooms are double occupancy, have their own sink, and share a bathroom with only one other room. It turns out I could have cut down on my packing since I did not need a robe to wear from the community shower to my room. Now I only had to share a bathroom with three other people. I will post pictures of the base and dorms in the coming weeks. So far my room remains a single, but I have been assured that I will have a new roommate with the next C-17 transport.
After unpacking, I met my colleagues coming back from the Long Duration Balloon (LDB) Facility at the galley for dinner. More to come on LDB and meals in my posts ahead. I went to the gym for a run on the treadmill and then to the Coffee House to play games with my friends and colleagues.
NASA’s Global Climate Change website gets a lot of user feedback. Aside from typical random Internet trolls and students posing thinly veiled attempts at getting us to write their term papers, one of the most commonly asked questions goes something like this:
“Hey, NASA, are you really sure people are causing climate change? Have you double-checked?” or “Hey, NASA, I have an idea. Maybe climate change is caused by x, y, z and it’s not really caused by humans. You should look into this.”
The short answer to this type of question is “Yes, we’ve double-, triple-, quadruple-checked. It’s science! We check and recheck a gazillion times. We’ve looked into everything you could possibly imagine and more. Before we commit to what we say, we have a strong desire to make sure it’s actually true.”
One example of how careful we have to be is when we’re analyzing the carbon dioxide in Earth’s atmosphere from space.
OCO-2 is the NASA mission designed to be sensitive enough to detect a single part of carbon dioxide per million parts of atmosphere (ppm). The way it works is super complicated. And because carbon dioxide is the most important human contribution to climate change (the biggest issue of our time) and expectations of science results were set very high, we have to be super-duper certain our measurements are correct.
The sensitivity makes it very challenging.
The instruments on OCO-2 not only measure the absolute amount of carbon dioxide at a location, but they also look for very small gradients in the distribution of CO2, the difference in the distribution of carbon dioxide between one location and another as a function of time. For example, “a gradient on and off a city is like 2 parts per million,” explained Mike Gunson, project scientist for the mission. "You see 2 parts per million from any city of modest size on up. You’re looking at the difference between 399.5 and 401.5 parts per million. So you have to be careful. Nobody’s done this over New York City, Mumbai, Beijing or Shanghai, where it could be wildly different.”
Scientists spend their lives working to get reliable data. Science is hard; it’s not a walk in the park. Everything doesn't just land in your lap. Sometimes it’s a miracle to get any data at all. People don’t often talk about the challenges of doing science, but if you could uncover the history of any project, you would probably find loads of problems, issues and challenges that come up.
After most NASA satellite launches, the instruments typically go through a validation phase, a two- or three-month period when engineers and project managers check, double-check and recheck the data coming in from the satellite to assess its quality and make sure it’s absolutely accurate before it’s released to the scientific community. But with OCO-2, “there is no validation phase,” Gunson told me, “because the measurements have such sensitivity. You’re always validating. Constant validation is an integral part of ensuring the integrity of the dataset.”
For OCO-2 to make an observation, the sky has to be clear, without clouds. Too much wind will move the carbon dioxide, so you also need quiet meteorological conditions. Then, before we can make an inference, we must assess the quality of data, which involves exceptionally large computing capacity.” Because there is so much data coming in, you end up using all sorts of analysis techniques, including machine learning, to analyze the quality of the data. OCO-2 launched in July 2014, and since this past September the data have been released to the broader science community to sink their teeth into. This means, Gunson said, “after a year of alligator-wrestling, all of a sudden we can walk it on a leash.”
Learn more about NASA’s efforts to better understand the carbon and climate challenge.
I look forward to your comments.
After arriving at my hotel in Christchurch around 1 a.m., I was up and on a shuttle to the Clothing Distribution Center (CDC) at 8:15 a.m. There we had an orientation session in the US Antarctic Passenger Terminal and were issued our Extreme Cold Weather (ECW) gear. (You'll notice that those of us in science enjoy our TLAs (three letter acronyms)!) The gear includes BIG RED (my favorite parka), wind pants, hats, gloves, goggles, fleece base layers, and bunny boots. The orientation procedures included a computer check to make sure that we don't bring any viruses that could infect the network in McMurdo as well as a form to make sure we had all received our flu vaccinations.
After the CDC, we had the rest of the day off. I met up with my friend Eric from the University of Arizona, his wife Valerie, and my colleague Craig, who was also heading down to the ice with me. Upon my request, we wandered down to the Rose Garden. Since there are no plants in Antarctica, I really wanted one last chance to smell the roses (literally!). From there we walked through a park in bloom with beautiful flowers and birds to the center of town.
Due to a series of devastating earthquakes in 2010 and 2011 the town center was cordoned offthe last time I was in Christchurch. The city has been rebuilding slowly, and now the center has been reopened and most of the unsafe, damaged buildings have been imploded. There's a cathedral in the center (shown below) with reinforcements. It is still not safe to enter, and the only picture I could take was through a chain link fence. From there, we went to the only cathedral left standing -- called the Cardboard Cathedral. I honestly do not understand the reason it is called the Cardboard Cathedral, but it was the only thing left undamaged in the town center after the earthquakes.
We had an early dinner at Maharaja Indian Restaurant next to our hotel. To my disappointment, my last sunset until January was clouded over and I didn't see much. I will have to wait until I return to Christchurch for the next one. I went to bed early for a 4:45 a.m. pickup for my ice flight!
On Thursday evening, I boarded Qantas Flight 18 from LAX to Sydney, Australia. The Boeing 747 departed just after midnight and landed in Sydney on Saturday morning. I had a 9.5 hour layover in Sydney, so I went through customs in Australia, checked my large carry-on bag at the airport, and took the train to Circular Quay (the Aussie pronunciation is Circle Kay). There, I wandered around the famous Sydney Opera House and Royal Botanical Gardens.
See the slideshow above for photos of my adventures around Sydney.
After a nice afternoon, I boarded my evening flight to Christchurch, New Zealand. The flight landed around midnight, and after going through customs in New Zealand, where I had to convince the agents that my JPL hardware would not harm sheep, I finally arrived at my hotel at 1 a.m. Door-to-door travel time was around 32 hours. I was on empty and enjoyed a short night’s sleep before waking up to go to the Clothing Distribution Center the following morning. Stay tuned for my next post!