Scientific Seen

News, Commentary, and Tutorials from a Scientific Perspective

Imagine the fuel bill for the Space Shuttle. It’s hard enough to fill your car with 16 gallons of ordinary gas, so imagine the cost to fill a 526,000-gallon tank with rocket fuel. And that’s just to ferry a satellite into orbit. Once in orbit, satellites have to jet themselves around with fuel they’ve brought themselves. Space travel is expensive and there’s a constant search for less costly means of propulsion.

The thrust generated by a propulsion system is proportional to the mass of the propellant multiplied by its velocity. That is, a spacecraft sending 50 grams of propellant away at 3 meters per second has the same thrust as another sending 25 grams away at 6 meters per second. That’s the idea behind electric propulsion: Use less mass than traditional propulsion systems, yet expel it more rapidly. And bringing less mass into Earth’s orbit means the spacecraft is lighter, so it needs less expensive rocket fuel to the begin with.

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Originally published at eHow, SEP 2011

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It would be difficult to think of a part of human life that is not affected by the information that satellites carry. Satellites watch the weather, carry telephone signals and provide navigation information for land, air and sea traffic. A satellite’s orbit should match its task. A long-term weather observation satellite should be in a high, geosynchronous orbit so it can continuously monitor a face of the Earth, while navigation satellites might find lower orbits more efficient. The task of adjusting a satellite’s orbit is an orbital mechanics problem, and one of the most common orbital mechanics problems is changing a coplanar orbit.

A satellite’s orbit is determined by its location and its velocity. So two satellites that go through the exact same point can have completely different orbits if their velocities are different. That’s the trick for changing coplanar orbits. At one point in a satellite’s orbit, change its velocity to put it into a different orbit. Then let it go for a while until it gets where you want it to end up and change its velocity again to put it into its final orbit. The details are not all that complicated, given a few key equations.

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Originally published at eHow, AUG 2011

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To maximize the amount of data returned by space missions such as the Cassini-Huygens mission to Saturn’s moon Titan, compression techniques are used to reduce the transmission size. But a minor miscalculation regarding the effect of the Doppler shift on the radio signal used by the Cassini orbiter and Huygens probe nearly prevented the acquisition of a significant fraction of the mission data. Engineers at NASA and the European Space Agency have devised a solution, but the problem might not have arisen if the probe had had the bandwidth to transmit large amounts of data without the need for aggressive compression.

Researchers at the Jet Propulsion Laboratory are investigating an approach that could make such a problem a thing of the past: deep-space laser communications. The high frequency and small divergence of laser beams make it possible to reduce receiver and transmitter apertures and to lower electrical power requirements while increasing data rates by an order of magnitude.

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Originally published in Photonics Spectra, SEP 2001

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As darkness falls, a solitary man trudges up the hillside to a lonely domed building. His breath sends clouds of mist into the chilly air as he enters the building and flicks a switch, splitting the dome open to reveal the night sky. He walks up to the 20-foot telescope, puts his eye to the eyepiece and views the mysteries of the universe.

The lonely astronomer at the telescope remains the prototypical icon of scientific exploration. Yet the next decade’s crown jewel of astronomy would distort abominably if a human breath crossed its field or the heat from a nearby human hand struck its mirrors. No lone astronomer will peer through its eyepiece at the heavens; instead, scientists and engineers at a control room in Maryland will operate it with collaborators from around the world. And there will be no lonely walk up the hillside, because this telescope will be nearly four times as far away as the moon…

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Originally published in Photonics Spectra, AUG 2001

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One justification for the multibillion-dollar International Space Station is that it is an orbiting laboratory. Rather than constructing a different satellite to conduct each experiment, researchers can use the resources on the space station. It would be desirable, however, to have station personnel perform the work with the virtual assistance of the researchers on the ground.

To do this, high-fidelity information would have to be available to the earthbound scientists, such as detailed visuals over a high-definition television feed. This capability does not yet exist, but a California company is working to change that.

DreamTime Inc. plans to send a high-definition television camera to the space station this summer. The initial flight will certify the camera, battery charger and film for space- flight. It will provide the opportunity to downlink frames intermittently and could allow some video over NASA’s Ku-band, but most video will be unavailable until the film is returned to Earth.

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Originally published in Photonics Spectra, JUL 2001

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