Deap Space Navigation

Does anyone know how we navigate our deep space probes? I know we use radar
and GPS in LEO. What do we use for deep space? My guess is we use Doppler
shift a lot -- but that is just a guess.

My understanding is the navigation system of the probe that had the unit
conversion error was "telling" us that there was a problem, but we didn't
have enough confidence in the navigation system to realize there was a
catastrophic error in the trajectory.

Danny Dot
www.mobbinggonemad.org

There are many different ways.

Some take pictures of objects, usually certain bright asteriods. There is
also a world network of recievers working like opposite to GPS.

Does anyone know how we navigate our deep space probes? I know we use
radar and GPS in LEO. What do we use for deep space? My guess is we use
Doppler shift a lot -- but that is just a guess.

My understanding is the navigation system of the probe that had the unit
conversion error was "telling" us that there was a problem, but we didn't
have enough confidence in the navigation system to realize there was a
catastrophic error in the trajectory.

Since the way they pass from one peice of software to the next and there
errors were all in that software as well no-one thought better.

I seem to recall a nasty cartoon around that time to the effect of.

Two astronauts hurtling to their doom and a tech on the ground with a kind
of Eureka balloon which said, Damn, I wondered what that extra set of
brackets did...

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Dac" wrote in message
u...
There are many different ways.

Some take pictures of objects, usually certain bright asteriods. There is
also a world network of recievers working like opposite to GPS.

Does anyone know how we navigate our deep space probes? I know we use
radar and GPS in LEO. What do we use for deep space? My guess is we use
Doppler shift a lot -- but that is just a guess.

My understanding is the navigation system of the probe that had the unit
conversion error was "telling" us that there was a problem, but we didn't
have enough confidence in the navigation system to realize there was a
catastrophic error in the trajectory.

Since the way they pass from one peice of software to the next and there
errors were all in that software as well no-one thought better.

In article ,
Danny Dot wrote:
Does anyone know how we navigate our deep space probes? I know we use radar
and GPS in LEO. What do we use for deep space? My guess is we use Doppler
shift a lot -- but that is just a guess.

The dominant method is radio tracking -- radar, but with the assistance of
the probe to repeat the signal back. (Normal radar is useless for such
small objects at such distances.) Round-trip time gives range, and Doppler
shift gives range rate (velocity along the probe-Earth line); these can
both be measured extremely accurately. More subtly, the *change* in
Doppler shift as the Earth rotates can be used to determine direction,
although not as accurately. These measurements are combined using a
sophisticated estimating process that looks at how the measurements
*should* be changing for a given trajectory, and solves simultaneously
for the most likely probe position/velocity and the most likely values of
other parameters (masses of planets, errors in measurements, etc.).

Some other techniques sometimes get added. If multiple ground antennas
are available *and* the probe's signal is a strong one, interferometry can
be used to measure direction *extremely* accurately. Maneuvers can be
measured by onboard accelerometers for comparison with tracking data. And
if the probe has a suitable camera, images showing planet(s) against a
star background can be used to establish position; this "optical
navigation" is especially useful when approaching a planet, because it
gives an independent check on position relative to the planet, which is
what you mostly care about.

My understanding is the navigation system of the probe that had the unit
conversion error was "telling" us that there was a problem, but we didn't
have enough confidence in the navigation system to realize there was a
catastrophic error in the trajectory.

Kind of, sort of. That was Mars Climate Orbiter. The units error messed
up the estimation of a growing trajectory error caused by small thruster
firings. The probe itself was not doing its own navigating. It *was*
computing better thruster-firing estimates than the ones produced on the
ground, but the navigation team wasn't aware of this and wasn't using the
results.

The MCO radio-navigation data wasn't behaving *quite* as it should have,
but there were other problems with using the data in the beginning, the
error happened to be in a direction that routine tracking wasn't very
sensitive to, and the small anomalies weren't conspicuous enough to alert
the navigators. (People *did* notice that something wasn't quite right,
but heavy workloads prevented prompt investigation of problems that didn't
seem serious.) VLBI wasn't used because the antenna time needed for it is
not simple to arrange, and MCO was seen as a routine mission that didn't
need special measures. And although MCO had a small camera, it wasn't
really very suitable for optical navigation and so none was attempted.

At the last minute, as MCO approached Mars and Mars's gravity began to
affect it, the discrepancies started to grow: Mars wasn't affecting the
trajectory quite as expected. The navigators started making corrections,
but they were busy and didn't have time to investigate properly, and the
severity of the underlying error -- and thus the size of the correction
that was really needed -- wasn't obvious until it was too late.

The real problem wasn't the units error, but the overworked team, the
persistent failure to investigate small but unexplained discrepancies, and
complacency based on the belief that entering Mars orbit was routine.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

"Henry" == Henry Spencer writes:

Henry The dominant method is radio tracking -- radar, but with the
Henry assistance of the probe to repeat the signal back. (Normal
Henry radar is useless for such small objects at such distances.)
Henry Round-trip time gives range, and Doppler shift gives range rate
Henry (velocity along the probe-Earth line); these can both be
Henry measured extremely accurately. More subtly, the *change* in
Henry Doppler shift as the Earth rotates can be used to determine
Henry direction, although not as accurately. These measurements are
Henry combined using a sophisticated estimating process that looks at
Henry how the measurements *should* be changing for a given
Henry trajectory, and solves simultaneously for the most likely probe
Henry position/velocity and the most likely values of other
Henry parameters (masses of planets, errors in measurements, etc.).

This was a great help, but now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

It seems that MCO could have used some way of measuring it's distance
from Mars more accurately, not just the measurement of it's vector in
comparision to Earth.

Now that we have a bunch of orbiters, would it be cost effective to
have some sort of small beacon put onto them so that they can help
other approaches?

John

John Stoffel wrote:"This was a great help, but now that we have more
and more deep space probes, and with the DSN network starting to get
overloaded, how would you make it easier to send probes so that they
can do more of their own navigation work?
Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could use
for it's own orbital insertion maneuvers?
It seems that MCO could have used some way of measuring it's distance
from Mars more accurately, not just the measurement of it's vector in
comparision to Earth.
Now that we have a bunch of orbiters, would it be cost effective to
have some sort of small beacon put onto them so that they can help
other approaches? John"


With respect to youre last question, the Deep space 1spacecraft had the
small deep-space transponder SDST on board, which advanced transponder
technology in an effort to reduce the demand on the deep space network
from traveling space probes.


http://nmp.nasa.gov/ds1/index.html
"Deep Space 1 launched from Cape Canaveral on October 24, 1998.
During a highly successful primary mission, it tested 12 advanced,
high-risk technologies in space. In an extremely successful extended
mission, it encountered Comet Borrelly and returned the best images and
other science data ever from a comet. During its fully successful
hyperextended mission, it conducted further technology tests. The
spacecraft was retired on December 18, 2001.
...ADVANCED TECHNOLOGIES..
http://nmp.nasa.gov/ds1/tech/transponder.html
SMALL DEEP SPACE TRANSPONDER
DS1 validated a small deep-space transponder (SDST), built by Motorola
that combines the receiver, command detector, telemetry modulator,
exciters, beacon tone generator, and control functions into one 3-kg
package. The SDST allows X-band uplink and X-band and Ka-band downlink.
To achieve the SDST's functionality without a new technology
development would require over twice the mass and 4 or 5 individual
subassemblies.
The SDST generates the tones needed for beacon monitor operations,
conceived to reduce the large demand that would be expected on the Deep
Space Network if many missions were in flight simultaneously, as
envisioned by NASA. The SDST continues to operate as planned."

tom

(Henry Spencer) wrote:

In article ,
Danny Dot wrote:
Does anyone know how we navigate our deep space probes? I know we use radar
and GPS in LEO. What do we use for deep space? My guess is we use Doppler
shift a lot -- but that is just a guess.

The dominant method is radio tracking -- radar, but with the assistance of
the probe to repeat the signal back. (Normal radar is useless for such
small objects at such distances.) Round-trip time gives range, and Doppler
shift gives range rate (velocity along the probe-Earth line); these can
both be measured extremely accurately. More subtly, the *change* in
Doppler shift as the Earth rotates can be used to determine direction,
although not as accurately. These measurements are combined using a
sophisticated estimating process that looks at how the measurements
*should* be changing for a given trajectory, and solves simultaneously
for the most likely probe position/velocity and the most likely values of
other parameters (masses of planets, errors in measurements, etc.).

Some other techniques sometimes get added. If multiple ground antennas
are available *and* the probe's signal is a strong one, interferometry can
be used to measure direction *extremely* accurately. Maneuvers can be
measured by onboard accelerometers for comparison with tracking data. And
if the probe has a suitable camera, images showing planet(s) against a
star background can be used to establish position; this "optical
navigation" is especially useful when approaching a planet, because it
gives an independent check on position relative to the planet, which is
what you mostly care about.

Damm - it's amazing how close that description is to the methods we
used to track targets using sonar. (Though our targets were usually
assumed to be non-cooperative.)

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

In article ,
John Stoffel wrote:
...now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

DSN is not just starting to get overloaded -- it's been overloaded for
some time now, actually.

Out in interplanetary space, more-or-less autonomous navigation using
optical-navigation techniques is not that hard. Deep Space 1 demonstrated
it successfully. (Actually, Apollo demonstrated it successfully, but the
unmanned-spacecraft guys tend to forget that.) Approaching a planet is the
iffy part.

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

In the long run, such things could help, at least for busy destinations,
but you need to invest substantial resources to build a GPS equivalent at,
say, Mars.

It seems that MCO could have used some way of measuring it's distance
from Mars more accurately, not just the measurement of it's vector in
comparision to Earth.

Optical navigation would have helped MCO more, I'd think. Inadequate
distance from Mars was MCO's problem in the end, but it wouldn't show up
very strongly in distance measurements until you were quite close, and you
really want to correct for it earlier than that.

Now that we have a bunch of orbiters, would it be cost effective to
have some sort of small beacon put onto them so that they can help
other approaches?

The data-relay package of the latest Mars orbiter, MRO, apparently has
some navigation capability, possibly useful during approaches.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

John Stoffel wrote:
This was a great help, but now that we have more and more deep space
probes, and with the DSN network starting to get overloaded, how would
you make it easier to send probes so that they can do more of their
own navigation work?

Would it help to put some sort of navigation beacon on the surface of
the target planet/moon? Something that the approaching probe could
use for it's own orbital insertion maneuvers?

I think the easiest solution would be to upgrade the DSN (I.E. add
more antennas and site). It's _much_ easier to repair/replace/upgrade
the hardware than beacons located in space.

D.
--
Touch-twice life. Eat. Drink. Laugh.

-Resolved: To be more temperate in my postings.
Oct 5th, 2004 JDL

In article ,
Derek Lyons wrote:
The dominant method is radio tracking... These measurements
are combined using a sophisticated estimating process...
Some other techniques sometimes get added...

Damm - it's amazing how close that description is to the methods we
used to track targets using sonar. (Though our targets were usually
assumed to be non-cooperative.)

Somewhat the same problem, of course, apart from whether the target is
trying to help. There may well have been some cross-fertilization on
methods -- probably mostly from NASA to the USN, given the security issues
for information traveling the other way. NASA threw money at these issues
in the early 60s, around the time when the USN was starting large-scale
deployment of gear intended to counter Soviet nuclear subs, including the
beginnings of sophisticated sonar, so the time scale was about right.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |