The founder of the Atmospheric Infrared Sounder Mission, Team Leader Dr. Moustafa T. Chahine

The founder of the Atmospheric Infrared Sounder Mission, Team Leader Dr. Moustafa T. Chahine, leaves behind a distinguished legacy of science, discovery, mentorship, and deep friendship. Beyond a career rich in accomplishment, Mous was a dear friend and colleague to so many over his 50-plus-year career at the Jet Propulsion Laboratory.

Please kindly leave your thoughts and acknowledgments below. These messages will be gathered up and presented to Mous’ family at a later date.

For more on Mous, visit:
› Mous Chahine Memorial Web Page
› Best Views on Climate: Chahine’s Vision Lives On Through AIRS

By Marc Rayman

NASA’s Dawn spacecraft is less than five months away from getting into orbit around its first target, the giant asteroid Vesta. Each month, Marc Rayman, Dawn’s chief engineer, shares an update on the mission’s progress.

Artist’s concept of NASA’s Dawn spacecraft at the large asteroid Vesta. The mission is less than five months away from getting into orbit around the large asteroid, its first target.

Dear Pleasant Dawnversions,

Deep in the asteroid belt, Dawn continues thrusting with its ion propulsion system. The spacecraft is making excellent progress in reshaping its orbit around the sun to match that of its destination, the unexplored world Vesta, with arrival now less than five months away.

We have considered before the extraordinary differences between Dawn’s method of entering orbit and that of planetary missions employing conventional propulsion. This explorer will creep up on Vesta, gradually spiraling closer and closer. Because the probe and its target already are following such similar routes around the sun, Dawn is now approaching Vesta relatively slowly compared to most solar system velocities. The benefit of the more than two years of gentle ion thrusting the spacecraft has completed so far is that now it is closing in at only 0.7 kilometers per second (1600 mph). Each day of powered flight causes that speed to decrease by about 7 meters per second (16 mph) as their orbital paths become still more similar. Of course, both are hurtling around the sun much faster, traveling at more than 21 kilometers per second (47,000 mph), but for Dawn to achieve orbit around Vesta, what matters is their relative velocity.

It may be tempting to think of that difference from other missions as somehow being a result of the destination being different, but that is not the case. The spiral course Dawn will take is a direct consequence of its method of propelling itself. If this spacecraft were entering orbit around any other planetary body, it would follow the same type of flight plan. This unfamiliar kind of trajectory ensues from the long periods of thrusting (enabled by the uniquely high fuel efficiency of the ion propulsion system) with an extremely gentle force.

Designing the spiral trajectories is a complex and sophisticated process. It is not sufficient simply to turn the thrust on and expect to arrive at the desired destination, any more than it is sufficient to press the accelerator pedal on your car and expect to reach your goal. You have to steer carefully (and if you don’t, please don’t drive near me), and so does Dawn. As the ship revolves around Vesta in the giant asteroid’s gravitational grip, it has to change the pointing of the xenon beam constantly to stay on precisely the desired winding route to the intended science orbits.

Dawn will scrutinize Vesta from three different orbits, known somewhat inconveniently as survey orbit, high altitude mapping orbit (HAMO), and low altitude mapping orbit (LAMO). Upon concluding its measurements in each phase, it will resume operating its ion propulsion system, using the mission control team’s instructions for pointing its thruster to fly along the planned spiral to the next orbit.

› Continue reading Dawn Spacecraft Creeping Up on Vesta

By Julie Cooper

Each month in “Slice of History” we’ll be featuring a historical photo from the JPL Archives. See more historical photos and explore the JPL Archives at https://beacon.jpl.nasa.gov/.

Transition Pipe — Photograph Number 327-287A

This test setup was part of an investigation in 1954 of the stability of laminar pipe flow with respect to disturbances of different frequencies and amplitudes. A disturbance generator was developed using vibrating aluminum reeds and instruments measured how a small amplitude disturbance in the air flow changed as it propagated down the 115–foot length of a 2” aluminum pipe. It appears to be located in the concrete channel that was used in the 1940s as a hydrodynamic tank with a rocket-propelled towing car (the “Hydrobomb”). At the end of the room you can see metal rungs that were used to climb down into the channel when the water was drained.

This post was written for “Historical Photo of the Month,” a blog by Julie Cooper of JPL’s Library and Archives Group.