Tag: JPL

Dawn Sets Course for Higher Orbit

Dawn Sets Course for Higher Orbit

After studying Ceres for more than eight months from its low-altitude science orbit, NASA’s Dawn spacecraft will move higher up for different views of the dwarf planet.

Dawn has delivered a wealth of images and other data from its current perch at 240 miles (385 kilometers) above Ceres’ surface, which is closer to the dwarf planet than the International Space Station is to Earth. Now, the mission team is pivoting to consider science questions that can be examined from higher up.

After Dawn completed its prime mission on June 30, having surpassed all of its scientific objectives at Vesta and at Ceres, NASA extended the mission to perform new studies of Ceres. One of the factors limiting Dawn’s lifetime is the amount of hydrazine, the propellant needed to orient the spacecraft to observe Ceres and communicate with Earth. By going to a higher orbit at Ceres, Dawn will use the remaining hydrazine more sparingly, because it won’t have to work as hard to counter Ceres’ gravitational pull.

“Most spacecraft wouldn’t be able to change their orbital altitude so easily. But thanks to Dawn’s uniquely capable ion propulsion system, we can maneuver the ship to get the greatest scientific return from the mission,” said Marc Rayman, chief engineer and mission director, based at NASA’s Jet Propulsion Laboratory, Pasadena, California.

Dawn Sets Course for Higher Orbit

On Sept. 2, Dawn will begin spiraling upward to about 910 miles (1,460 kilometers) from Ceres. The altitude will be close to where Dawn was a year ago, but the orientation of the spacecraft’s orbit — specifically, the angle between the orbit plane and the sun — will be different this time, so the spacecraft will have a different view of the surface.

The mission team is continuing to develop the extended mission itinerary and will submit a full plan to NASA next month.

Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. For a complete list of mission participants.

source: world press news

Study Earth from Space

Study Earth from Space

That’s what radiofrequency engineers call the mysterious forces guiding communications over the air. These forces involve complex physics and are difficult enough to master on Earth. They only get more baffling when you’re beaming signals into space.

Until now, the shape of choice for casting this “magic” has been the parabolic dish. The bigger the antenna dish, the better it is at “catching” or transmitting signals from far away.

But CubeSats are changing that. These spacecraft are meant to be light, cheap and extremely small: most aren’t much bigger than a cereal box. Suddenly, antenna designers have to pack their “black magic” into a device where there’s no room for a dish — let alone much else.

“It’s like pulling a rabbit out of a hat,” said Nacer Chahat, a specialist in antenna design at NASA’s Jet Propulsion Laboratory, Pasadena, California. “Shrinking the size of the radar is a challenge for NASA. As space engineers, we usually have lots of volume, so building antennas packed into a small volume isn’t something we’re trained to do.”

Study Earth from Space


Challenge accepted.

Chahat and his team have been pushing the limits of antenna designs, and recently worked with a CubeSat team on the antenna for Radar In a CubeSat (RainCube), a technology demonstration mission scheduled for launch in 2018. RainCube’s distinctive antenna looks a little like an umbrella stuffed into a jack-in-the-box; when open, its ribs extend out of a canister and splay out a golden mesh.

As its name suggests, RainCube will use radar to measure rain and snowfall. CubeSats are measured in increments of 1U (A CubeSat unit, or 1U, is roughly equivalent to a 4-inch cubic box, or 10x10x10 cubic centimeters). The RainCube antenna has to be small enough to be crammed into a 1.5U container. Think of it as an antenna in a can, with no spare room for anything else.

“Large, deployable antennas that can be stowed in a small volume are a key technology for radar missions,” said JPL’s Eva Peral, principal investigator for RainCube. “They open a new realm of possibilities for science advancement and unique applications.”

To maintain its relatively small size, the antenna relies on the high-frequency, Ka-band wavelength — something that’s still rare for NASA CubeSats, but is ideally suited to RainCube. But Ka-band has other uses besides radar. It allows for an exponential increase in data transfer over long distances, making it the perfect tool for telecommunications.

Ka-band allows for data rates about 16 times higher than X-band, the current standard on most NASA spacecraft.

In that sense, the development of RainCube’s antenna can test the use of CubeSats more generally. While most have been limited to simple studies in near-Earth orbit, the right technology could allow them to be used as far away as Mars or beyond. That might open up CubeSats to a whole range of future missions.

“To enable the next step in CubeSat evolution, you need this kind of technology,” said JPL’s Jonathan Sauder, mechanical engineer lead for the RainCube antenna.

Chahat was brought on to the RainCube team after he worked on another innovative antenna design. The MarCO (Mars Cube One) mission consists of a pair of Cubesats that have been proposed to fly in 2018 with NASA’s InSight lander, which would measure the Red Planet’s tectonics for the first time. While InSight is touching down, the two MarCO CubeSats would relay information about the landing back to Earth. Just like RainCube, MarCO is primarily a technology demonstration; it would test how future missions could use CubeSats to carry communication relays with them, enabling researchers to know what’s happening on the ground much faster.

The MarCO design looks nothing like a typical antenna. In place of a round dish are three flat panels dotted with reflective material. The shape and size of these dots form concentric rings that mimic the curve of a dish. Just as a dish might, this mosaic pattern of dots focuses the signal radiated from the antenna’s feed towards Earth.

“New technologies like these allow NASA and JPL to do more with less,” said JPL’s John Baker, program manager for MarCO. “We want to make it possible to explore anywhere we want in the solar system.”

Both RainCube and MarCO highlight creative workarounds to the size limits of CubeSats. The next trick for Chahat and his colleagues will be combining those designs into an even bigger antenna: a reflectarray ranging 3.3 feet by 3.3 feet (1 meter by 1 meter) and made up of 15 flat panels. These segmented panels would unfold like the flat surface of MarCo’s, while the antenna’s feed would telescope out like RainCube’s antenna. This antenna would be called OMERA, short for the One Meter Reflectarray.

“If we can extend the technology to one meter in size, the OMERA antenna will push the limits of what can be practically flown today on a CubeSat,” said Tom Cwik, manager of space technology at JPL.

A prototype of the OMERA CubeSat is expected to be ready by March of 2017.

“OMERA’s larger array will produce higher gain for telecommunications applications, or will produce narrower beam widths for Earth science needs,” Chahat said. That means we would be able to venture even farther into deep space and will have even more powerful and accurate radars.”

Caltech in Pasadena, California, manages JPL for NASA.

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