[Sis-csi] Interplanetary distance laser link

[Krupiarz, Christopher]

Lloyd,

No, it's not possible to do so.  Something to note, though, is even if it were we'd be hard pressed to keep up due to our processor, its load, and (at least in part, I'm sure) in how we implemented CFDP and our telemetry system.  Leigh Torgerson and his team at JPL have done some really nice work in this area by placing CFDP on an FPGA which would handle such high rates with bandwidth to spare.

Chris


-----Original Message-----
From: sis-csi-bounces at mailman.ccsds.org on behalf of Lloyd Wood
Sent: Fri 1/6/2006 7:59 PM
To: dtn-interest at mailman.dtnrg.org
Cc: sis-csi at mailman.ccsds.org
Subject: [Sis-csi] Interplanetary distance laser link
 
Chris (Krupiarz), since Messenger has a CFDP implementation, is your
crew going to try running CFDP over this?

Details in attached Science paper:
Two-Way Laser Link over Interplanetary Distance, David E. Smith, Maria
T. Zuber, Xiaoli Sun,1 Gregory A. Neumann, John F. Cavanaugh, Jan F.
McGarry, Thomas W. Zagwodzki, Science vol. 311, p. 53, 6 January 2006.
Supplementary material at:
http://www.sciencemag.org/cgi/content/full/311/5757/53/DC1

http://www.space.com/missionlaunches/060104_laser_comm.html

Record Set for Space Laser Communication
By Ker Than
Staff Writer
posted: 05 January 2006
02:11 pm ET

In a cosmic version of laser tag, NASA's MESSENGER spacecraft and an
Earth-based observatory successfully exchanged laser pulses with each
other while millions of miles apart.

The feat sets a new record for laser transmission in space, a process
which may one day be used to communicate across interplanetary
distances and provide scientists with a powerful tool to measure the
movement of planets and test fundamental principles in physics.

MESSENGER was launched in 2004 on a six-year voyage to Mercury. In
late May of 2005, scientists used the spacecraft's Mercury Laser
Altimeter (MLA), an instrument designed to map Mercury's surface, to
exchange laser pulses with NASA's Goddard Geophysical and Astronomical
Observatory in Maryland. MESSENGER was approximately 15 million miles
(25 million km) away at the time.

The experiment, reported today, marks the first successful
back-and-forth exchange of laser signals between Earth and space. In
1992, laser pulses were successfully transmitted from Earth and
detected by a receiver aboard the Galileo probe while it was about 4
million miles (6 million km), but the transmission was only one way
since Galileo did not have a transmitter of its own.

Broadband in space

Two-way laser communication in space has long been a goal for NASA
because it would enable data transmission rates that are 10 to 1,000
times higher than traditional radio waves. While lasers and radio
transmissions both travel at light-speed, lasers can pack more data.
It's similar to moving from a dial-up Internet connection to
broadband.

"We've been trying to do this kind of thing for about a decade," said
David Smith, a researcher from Goddard Space Flight Center who was
involved in the experiment. "We attempted to do it on one of our Mars
probe but either we got weathered out or the spacecraft misread some
stars and everything closed down."

The Mars Telecommunications Orbiter spacecraft, set to launch in 2010,
but cancelled last summer due to budget problems, would have used
lasers to transmit data between Earth and Mars at a rate of between 1
to 30 million bits per second, depending on how close the two planets
are to each other.

Currently, the maximum data rate between Earth and Mars is about
128,000 bits per second.

Laser tag in space

A major challenge with laser communications in space is keeping
transmitter and receiver locked onto each other. This is like trying
to aim the beam of a very strong laser pointer, akin to the type used
in a conference room, at a target millions of miles away.

Radio waves radiate outwards from a transmitter in spherical ripples
rather than pencil-thin beams like lasers. So the receiver and
transmitter in a laser-based communication system have to be pointed
very precisely.

"You don't need to do that with [radiowaves],"  Smith said. "The beam
divergence is sufficiently large that if you point the antenna at
about the right place, and if you're within half a degree, you're
usually in great shape."

Laser ruler

If the technical hurdles can be overcome, lasers would benefit not
only communications, but basic science as well. Astronomers could use
lasers like very accurate rulers to measure the movement of planets
with unprecedented precision.

"With microwaves, we're limited to numbers like a meter or two in
distance, whereas [lasers have] a potential for getting down into well
beyond the centimeter range," Smith told SPACE.com.

Lasers could also be used refine basic principles of fundamental physics.

"If you could make planetary scale measurements at the centimeter or
millimeter level­which we can't at the moment­then we could understand
some principles of relativistic physics which can only be tested at
very extreme accuracies at very large distances," Smith said.

The record-setting effort is described in the Jan. 6 issue of the
journal Science.

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