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Music

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How does the atomic

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clock play a role for deep space

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navigation? Well today atomic

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clocks are central to deep

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space navigation it's just

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that those clocks are on the

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ground. And so an atomic clock

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generates a signal and it is sent

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through the antennae on the

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ground to a spacecraft in deep

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space. And that signal is

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turned around and received back

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at the transmitting. And

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with that transmission of the

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signal we can do measurements

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of that signal. You know how the

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doppler shift on the signal

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is how we can know how fast

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the spacecraft is moving and

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how long that signal takes is a

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measure of how far that spacecraft

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is. So the deep space atomic

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clock can change that paradigm.

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It can originate the signal

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at the earth and it can end

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at the spacecraft. Its good

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enough, that small clock that

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we are building is as stable and

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accurate as the ground clock

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that originated the signal.

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We get to utilize some of the

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effiences that the deep space

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tracking network has to offer

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today. The DSN supports more

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downlinks than it does uplink

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and so at places like Mars

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where  we have a number of

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spacecraft that are competing for

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two-way tracking time... you

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don't have to do that anymore.

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What does that do for us? well

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what we have found with a 2

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times increase in our

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tracking data for a Mars orbiter,

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the orbit information that

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we get is improved upon by a

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factor of five. One of the things

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we are envisioning at Mars is

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landing a pin-point lander,

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one that can land to a very

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precise location (beep sounds)

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on the surface of Mars. there's

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a lot of steps into making

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that happen. One of which is

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entering the top of the atomosphere

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and taking your entry state

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knowledge and onboard flying

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a trajectory with that entry

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state knowledge. We way in

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which we upload that navigation

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state today is that we do all

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the processing on the ground

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in about six or so hours and

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before entry we upload a final

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nav state to the vehicle. Well

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you can imagine after six hours

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of flight that solutions is little

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stale when you get to the top

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of the atmosphere. Well with DSAC

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with the measurement happening

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onboard you don't have to suffer

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that six hour delay. You can be

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computing onboard in real time.

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And what that does is where the

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six hour solution is in error by

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a few kilometers, this solution

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that's onboard is only off by a

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handful meters. that has a real

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benefit to decreasing the amount

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of propellant you have to carry to

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then later fly out the errors

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you had when you didn't know where

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you were at when you originally

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were at the top of the atmosphere.So

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that's gonna open up new ways,

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new science we are going to be

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able to do. In fact it's going

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to improve the gravity science we

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are going to be able to do at

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Mars today. An example of gravity

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science improvement that the clock

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enables further out is NASA is

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envisioning going to Europa, a

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moon around Jupiter, and one of the

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fundemental things we want to

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learn about Europa is if there is an

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ocean under the crustal ice that

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we see at Europa? Well gravity

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science is a way in which we can

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make that determination; if there

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is an ocean underneath. And to

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be able to do the measurement, the

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gravity science measurement that

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NASA is planning. They're going

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to do it, one approach is a

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flyby mission. So they will fly by

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Europa with a four hour tracking

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pass, and then have a thirty day

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orbit around Europa, and then

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come back again for another flyby.

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And do a sequence of thirty or so

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of these flybys. Well if we have

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the atomic clock on a downlink

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signal from that flyby and it's

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received at the earth we can do

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it at Ka band. and the benefit of

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going to Ka band isn't so much

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that it has to deal with we can

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increase the bandwidth but what

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it does do is that it improves the

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accuracy of the measurement that

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we are taking, and it improves it

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by an order of magnitude and that

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is fundemental. Its that improvement

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in the data quality that will

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allow us to determine the gravity