Raumfahrt - NASAs Europa Clipper Mission -Update-1


NASA to replace Europa Clipper instrument



WASHINGTON — NASA has removed an instrument previously selected for the Europa Clipper mission, citing cost growth, but will seek ways to replace it with a less complex design.

In a March 5 statement, NASA said that it would no longer pursue development of the Interior Characterization of Europa Using Magnetometry (ICEMAG) instrument, a magnetometer designed to measure the magnetic field around the icy moon of Jupiter. ICEMAG was one of nine instruments originally selected by NASA in 2015 for development for the Europa Clipper mission.

NASA said that the increasing cost of ICEMAG, still in its preliminary design phase, led to its removal from the mission. “I believe this decision was necessary as a result of continued, significant cost growth and remaining high cost risk for this investigation,” Thomas Zurbuchen, NASA associate administrator for science, said in a memo.

In that memo, he said that ICEMAG exceeded a “cost trigger” last summer that had been put in place for it and other instruments to keep costs under control. That cost trigger escalated reviews of the instrument all the way to NASA Headquarters, including a briefing there Feb. 14. The key problem with the instrument was accommodating its “scalar vector helium sensors,” used to measure the magnitude and direction of the magnetic field.

Zurbuchen said in the memo that, at the time of the February review, ICEMAG’s estimated cost has grown to $45.6 million, $16 million above its original cost trigger and $8.3 million above a revised cost trigger established just a month earlier. That cost was also three times above the original estimate in the ICEMAG proposal.

“The level of cost growth on ICEMAG is not acceptable, and NASA considers the investigation to possess significant potential for additional cost growth,” Zurbuchen wrote in the memo. “As a result, I decided to terminate the ICEMAG investigation.”

NASA will instead pursue options for “a simpler, less complex” magnetometer on Europa Clipper, although the announcement contained few details about how that will be accomplished. Scientists who were part of the ICEMAG team will be invited to remain on the overall mission science team.

“A magnetometer investigation brings significant value to Europa science and exploration,” Zurbchen said in the statement about ICEMAG’s removal. “We have enough time before launch to find such a replacement and will move quickly to implement this.”

Scientists consider the inclusion of a magnetometer particularly valuable for probing the interior of Europa, thought to contain a global ocean of liquid water. Data from the magnetometer on the Galileo spacecraft, which performed many flybys of Europa, detected variations in Jupiter’s magnetic field in the vicinity of the moon that scientists said were likely caused by the presence of an electrically conductive fluid, like water, beneath the surface.

Scientists had hoped ICEMAG would provide more detailed magnetic field measurements that could constrain the depth, thickness and salinity of the ocean. That would help scientists assess the potential habitability of Europa, a key goal of the overall Europa Clipper mission.

“The nature of the subsurface ocean and how it interacts with the surface is critical to evaluating Europa’s potential habitability,” Carol Raymond of JPL, the principal investigator for ICEMAG, said in a 2015 statement about the instrument’s selection. “Knowledge of the ocean properties helps us understand Europa’s evolution and allows evaluation of processes that have cycled material between the depths and the surface.”

Zurbuchen said that NASA was still committed to the overall Europa Clipper mission, but instituted the cost trigger process to manage the mission’s overall costs and avoid increases that could upset the overall balance of the agency’s planetary science programs. “We consider it a critical part of the mission portfolio of NASA Science, and am looking forward to see this development mature towards flight,” he wrote in the memo.

The Europa Clipper mission benefitted for years from the patronage of Rep. John Culberson (R-Texas), a House appropriator who became chairman of the subcommittee that funds NASA four years ago. Culberson was an unusually staunch advocate for both Europa Clipper and a follow-on lander, providing funding for the mission far above any NASA request for them. In the final fiscal year 2019 funding bill, passed in February but whose NASA provisions were finalized late last year, Europa Clipper received $545 million, more than double NASA’s request of $264.7 million.

Culberson, though, lost re-election last November. While NASA says it remains committed to flying Europa Clipper, the mission is unlikely to see the increased funding provided to accelerate its development. The 2019 spending bill set a 2023 deadline for launching the mission, a year later than previous bills, but NASA’s statement about the removal of ICEMAG said only that it plans to launch Europa Clipper “in the 2020s.”

Quelle: SN


Update: 3.04.2019


Europa Clipper High-Gain Antenna Undergoes Testing


A full-scale prototype of the high-gain antenna on NASA's Europa Clipper spacecraft is undergoing testing in the Experimental Test Range at NASA's Langley Research Center in Hampton, Virginia. Credit: NASA/Langley


It probably goes without saying, but this isn't your everyday satellite dish.

In fact, it's not a satellite dish at all. It's a high-gain antenna (HGA), and a future version of it will send and receive signals to and from Earth from a looping orbit around Jupiter.

The antenna will take that long journey aboard NASA's Europa Clipper, a spacecraft that will conduct detailed reconnaissance of Jupiter's moon Europa to see whether the icy orb could harbor conditions suitable for life. Scientists believe there's a massive salty ocean beneath Europa's icy surface. The antenna will beam back high-resolution images and scientific data from Europa Clipper's cameras and science instruments.

The full-scale prototype antenna, which at 10 feet (3 meters) tall is the same height as a standard basketball hoop, is in the Experimental Test Range (ETR) at NASA's Langley Research Center in Hampton, Virginia. Researchers from NASA's Jet Propulsion Laboratory in Pasadena, California, the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, and Langley are testing the prototype in the ETR in order to assess its performance and demonstrate the high pointing accuracies required for the Europa Clipper mission.

The ETR is an indoor electromagnetic test facility that allows researchers to characterize transmitters, receivers, antennas and other electromagnetic components and subsystems in a scientifically controlled environment.

"Several years ago we scoured the country to find a facility that was capable of making the difficult measurements that would be required on the HGA and found that the ETR clearly was it,"said Thomas Magner, assistant project manager for Europa Clipper at the Applied Physics Laboratory. "The measurements that will be performed in the ETR will demonstrate that the Europa Clipper mission can get a large volume of scientific data back to Earth and ultimately determine the habitability of Europa."

Tests on this prototype antenna are scheduled to wrap up soon; however, researchers plan to return to the ETR in 2020 to conduct additional tests on Europa Clipper's high-gain antenna flight article. Europa Clipper plans to launch in the 2020s, with travel time to Jupiter taking three to seven years (depending on the launch vehicle and which planetary alignments can be utilized).

JPL manages the Europa Clipper mission for NASA's Science Mission Directorate. The multiple-flyby concept was developed in partnership with the Applied Physics Laboratory.

Quelle: NASA


Update: 27.04.2019


Europa Clipper instrument change could affect mission science



WASHINGTON — A NASA decision last month to replace an instrument on the Europa Clipper mission with a less expensive, but less capable, alternative is leaving scientists concerned about the ability of the mission to meet some of its objectives.

NASA announced March 5 that it would end development of a magnetometer called the Interior Characterization of Europa Using Magnetometry (ICEMAG) for the mission, citing cost growth and risk of further overruns. At the time of the decision, NASA said the cost of the instrument had grown to $45.6 million, three times its original estimate.

In its place, NASA will fly a “facility magnetometer” that will collect some of the same magnetic field data as ICEMAG in the vicinity of Europa, an icy moon of Jupiter. The agency subsequently said Margaret Kivelson, a planetary scientist at UCLA who also is the new chair of the Space Studies Board, will lead the development of the magnetometer.

The facility magnetometer will lack components known as scalar vector helium sensors, whose development problems led to ICEMAG’s cost overruns. Robert Pappalardo, project scientist for the mission, said in an April 23 presentation at an Outer Planets Assessment Group (OPAG) meeting here that challenges with the sensors’ fiber optic cables, which are sensitive to the temperature and radiation conditions at Jupiter, “essentially brought on its downfall.”

Instead, the facility magnetometer will rely on more conventional fluxgate magnetometers. Those devices are very precise, Pappalardo noted, but suffer offset errors over time. He estimated the original ICEMAG scalar vector helium sensors would have provided an order of magnitude improved accuracy.

The increased errors of the fluxgate magnetometers, he said, “does put at risk” some of the key, or Level 1, science requirements of the mission, notably estimating the thickness of Europa’s ice shell as well as the depth and salinity of the liquid water ocean beneath the ice. Other Level 1 science requirements aren’t affected, he emphasized.

Pappalardo showed models of the difference between potential ICEMAG and facility magnetometer measurements. With the better performance of ICEMAG, he estimated the ocean depth could be known to an accuracy of 20 kilometers. With the facility magnetometer, “ocean depth would be very poorly known: somewhere between 20 to 100 kilometers,” he said of one particular case. “That’s not a lot of information over what we have now.”

The performance of the magnetometer will also be dependent on the conductivity of that ocean. “In a high-conductivity case, we won’t know much,” he said, because of much higher errors. “We’re going to have to hope that Europa cooperates or that we can beat down this error to closer to the ICEMAG requirement.”

Pappalardo said the magnetometer team is looking for ways to improve its accuracy. That could include periodic rolls of the spacecraft to measure the ambient magnetic field and better calibrate the magnetometer.


A proposed trajectory for the Europa Clipper that could allow it to reach Jupiter in less than six years without the thermal issues of alternative approaches that require a Venus flyby. Credit: NASA

Alternative launch plans

Overall, though, the Europa Clipper mission is moving ahead largely as planned. Lori Glaze, director of NASA’s planetary science division, said at the OPAG meeting that the mission is on track for a confirmation review this summer, at which point the agency will formally set a cost estimate.

Europa Clipper is now aiming for a launch in 2023, one year later than prior plans, a decision that project officials said was driven by workforce availability for the mission. Both NASA and Congress now support a 2023 launch date after years of debate where NASA sought to launch the mission later in the 2020s, if at all.

“I think this is one of the big wins from the president’s 2020 budget,” Glaze said. “We’re finally in sync between the president’s budget and Congress and we’re all in line with that advanced launch date of 2023.”

There’s still disagreement, though, on how to launch Europa Clipper. The fiscal year 2019 appropriations bill, as in previous years, mandated the use of the Space Launch System for the mission. SLS would allow the spacecraft to fly directly to Jupiter without the need for any gravity assists, arriving less than two and a half years after launch.

NASA’s fiscal year 2020 budget proposal, though, calls for using a commercially procured launch vehicle. That would require use gravity assist maneuvers and increase the travel time of the mission by several years, but NASA argued in its budget request that it would save “over $700 million” versus SLS.

The project has been looking at a number of options for the non-SLS option. Speaking at a National Academies committee meeting in March, Barry Goldstein, Europa Clipper project manager, said one option under consideration would be a launch on a SpaceX Falcon Heavy equipped with a Star 48BV kick stage. That trajectory, known formally as Delta-V Earth Gravity Assist 3-Minus, involves a launch in November 2023 and an Earth flyby in October 2025 prior to arrival at Jupiter in September 2029.

The travel time of a little less than six years is only slightly shorter than some other alternatives previously studied. However, it has the advantage of not requiring any gravity assist flybys of Venus, with the spacecraft getting only slightly closer to the sun on its trajectory than the Earth. “That solves a world of problems on thermal management,” Goldstein said. “We no longer have the challenge of the thermal problems that we had getting close to Venus.”

A second advantage, he said, is that it offers a backup launch window roughly a year later, whereas with the Venus flyby trajectory the mission would have to wait until 2025 if it can’t launch in 2023. “We’re not 100 percent there yet, but things are looking very positive” for the new trajectory, he said.

Lander uncertainty

The outlook is less positive for a follow-on lander mission to Europa. The 2019 appropriations bill included $195 million to work on the lander, directing NASA to launch it by 2025.

The fiscal year 2020 budget request, though, included no funding for the mission, just as had been the case in previous years. The budget proposal noted that the agency estimated a lander mission to cost as much as $5 billion, and that a midterm review published last year of the most recent planetary science decadal survey recommended that a lander mission “be assessed in the context of other planetary priorities in the next decadal survey.”

In previous years, Congress has added funding to the budget for a Europa lander. However, the mission’s most influential proponent, Rep. John Culberson (R-Texas), who had been chairman of the House appropriations subcommittee that funds NASA, lost reelection last November.

At the OPAG meeting, NASA’s Glaze said that the agency will use the funding appropriated for work on a Europa lander in 2019 to support key technology development that could support such a mission in the future.

“I can assure you that the funding that we do have is being directed towards lots of early technology development and risk mitigation to prepare for a future Europa lander,” she said. “What I always say is, it’s not if, it’s when.”

Quelle: SN