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Fine-Tuning New Horizons’ Trajectory

I love the timing of New Horizons’ next encounter, just as we begin a new year in 2019. On the one hand, we’ll be able to look back to a mission that has proven successful in some ways beyond the dreams of its creators. On the other hand, we’ll have the first close-up brush past a Kuiper Belt Object, 2014 MU69 or, as it’s now nicknamed, Ultima Thule. This farthest Solar System object ever visited by a spacecraft may, in turn, be followed by yet another still farther, if all goes well and the mission is extended. This assumes, of course, another target in range.

We can’t rule out a healthy future for this spacecraft after Ultima Thule. Bear in mind that New Horizons seems to be approaching its current target along its rotational axis. That could reduce the need for additional maneuvers to improve visibility for the New Horizons cameras, saving fuel for later trajectory changes if indeed another target can be found. The current mission extension ends in 2021, but another extension would get a powerful boost if new facilities like the Large Synoptic Survey Telescope become available, offering more capability at tracking down an appropriate KBO. Hubble and New Horizons itself will also keep looking.

But even lacking such a secondary target, an operational New Horizons could return useful data about conditions in the outer Solar System and the heliosphere, with the spacecraft’s radioisotope thermoelectric generator still producing sufficient power for some years. I’ve seen a worst-case 2026 as the cutoff point, but Alan Stern is on record as saying that the craft has enough hydrazine fuel and power from its plutonium generator to stay functional until 2035.

By way of comparison with Voyager, which we need to revisit tomorrow, New Horizons won’t reach 100 AU until 2038, nicely placed to explore the heliosphere if still operational.

But back to Ultima Thule, a destination now within 112 million kilometers of the spacecraft. New Horizons is closing at a rate of 14.4 kilometers per second, enroute to what the New Horizons team says will need to be a 120 by 320 kilometer ‘box’ in a flyby that needs to be predicted within 140 seconds. Based on what we saw at Pluto/Charon, these demands can be met.

Image: At left, a composite optical navigation image, produced by combining 20 images from the New Horizons Long Range Reconnaissance Imager (LORRI) acquired on Sept. 24. The center photo is a composite optical navigation image of Ultima Thule after subtracting the background star field; star field subtraction is an important component of optical navigation image processing since it isolates Ultima from nearby stars. At right is a magnified view of the star-subtracted image, showing the close proximity and relative agreement between the observed and predicted locations of Ultima. Credit: NASA/JHUAPL/SwRI/KinetX.

Above are the latest navigation images from New Horizons’ Long Range Reconnaissance Imager (LORRI). An engine burn on October 3 further tightened location and timing information for the New Year’s flyby, a 3 ½ minute maneuver that adjusted the spacecraft’s trajectory and increased its speed by 2.1 meters per second. Records fall every time New Horizons does this, with the October 3 correction marking the farthest course correction ever performed.

It’s interesting to learn, too, that this is the first time New Horizons has made a targeting maneuver for the Ultima Thule flyby that used pictures taken by New Horizons itself. The ‘aim point’ is 3,500 kilometers from Ultima at closest approach, and we’ve just learned that these navigation images confirm that Ultima is within 500 kilometers of its expected position.

“Since we are flying very fast and close to the surface of Ultima, approximately four times closer than the Pluto flyby in July 2015, the timing of the flyby must be very accurate,” said Derek Nelson, of KinetX Aerospace, Inc., New Horizons optical navigation lead. “The images help to determine the position and timing of the flyby, but we must also trust the prior estimate of Ultima’s position and velocity to ensure a successful flyby. These first images give us confidence that Ultima is where we expected it to be, and the timing of the flyby will be accurate.”

I’m already imagining New Year’s eve with Ultima Thule to look forward to. You can adjust your own plans depending on your time zone, but the projected flyby time is 0533 UTC on the 1st. As with Pluto/Charon, the excitement of the encounter continues to build. In the broader picture, the more good science we do in space, the more drama we produce as we open up new terrain. This week alone, we need to look at the Hayabusa2 operations at Ryugu, the upcoming OSIRIS-REx exploration of asteroid Bennu, and the continuing saga of Voyager 2.

But New Horizons also reminds us of an uncomfortable fact. When it comes to the outer system, this is the only spacecraft making studies of the Kuiper Belt from within it, and there is no other currently planned. Data from this mission will need to carry us for quite some time.

{ 21 comments… add one }
  • Charley October 8, 2018, 13:41

    A few questions as well as observations. First off Mr. Gilster , did use mean to say in the above paragraph “You can adjust your own plans depending on your time zone, but the projected flyby time is 0533 UTC on the 19th.” Did you mean to say the 19th?
    With regards to the targeting, while I can’t imagine this could be done on this mission as I don’t even think it’s equipped to do so; but on future missions could radar on the spacecraft be used to echo locate a planetary target, such that range/velocity measurements could be performed on the target and from that far greater accuracy be achieved for an anticipated flyby ? I can see that use of such radar would be a tremendous boon to target location as well as practice for what will be inevitably the use of forward-looking radar in collision avoidance for interstellar missions which will inevitably be expected to encounter millimeter and larger size obstructions in their flight paths.
    My second question, Mr. Gilster is would the flight operators of the New Horizons craft permit the targeting of a NEW Kuiper Belt Object , even if it would use up all the propellant, leaving no reserve fuel for fine tuning the trajectory with the hope of getting some further scientific payback ?

    • Paul Gilster October 8, 2018, 15:07

      Yipes, I’m glad you spotted that typo. I was clearly thinking ’19’ because of 2019. The flyby is, of course, on the 1st. Now fixed.

      On targeting, I don’t know what sort of leeway the controllers would build in re propellant, but I think maximizing the scientific return would always be the first priority, so I’m sure there is a great deal of flexibility built in.

      I’m afraid I don’t know the answer to your question about radar.

      • Laintal October 8, 2018, 16:04

        Thanks for the correction Paul I can continue with the New Years plans after all.

        New Horizons being a New Frontiers program mission a radar would have cost too much to include, and given the huge distance and small size of Ultima Thule, it would not have been powerful enough for observations until very close, at which point very little time would have been left for course corrections.

        I’m sure if they can find another target the mission will be extended :)

        • Charley October 9, 2018, 18:44

          Laintal-it often is a point of contention for me when radar is considered not viable for space missions. Why? Simply because in the case of a target such as the one that will be encountered on New Year’s Eve, you already know what its orbit is going to be (approximately) and as such a focused radar beam can be sent out which should permit range/velocity determinations of the target without necessarily requiring vast power.

          More to the point, if were going to engage in semi-relativistic spaceflight in interstellar voids we better darn well have some way of assessing what is going to be ahead of us. A focused radar along the flight path would seem to be almost a given and it would seem that we should bend every effort toward getting ourselves an ability to look “ahead.”

  • Laurel Kornfeld October 8, 2018, 13:58

    There are serious discussions underway about a return mission to Pluto, this time with an orbiter and lander. Such a mission could also study the environment in this part of the outer solar system.

  • Jim Baerg October 8, 2018, 14:51

    SpaceX is reducing the cost of doing anything above the atmosphere, & KiloPower should cut the cost of doing things beyond the asteroid belt. Those 2 technologies may mean we get more outer solar system missions sooner than you think.

  • Gary Wilson October 8, 2018, 16:53

    The flyby brings the probe to within 3500 km (2200 miles) of Ultima Thule I believe. Will the resolution of the pictures produced be as good as the flyby of Pluto? If so, it should be spectacular. A lander for Pluto seems a bit premature surely? We have targets closer in with far more promise (Europa, Enceladus, Ganymede, and Ceres to name but a few). Pluto does look fascinating but surely go for the low hanging fruit first?

    • Andrei October 10, 2018, 8:36

      They hope to get images of a similar quality. most in the approach.
      Images from 90 degree side not likely, from kosmos perspective this is a pebble drive past by speed train.

      Premature yes, and not serious. They do studies because Pluto is of current interest.
      One person say I want to do a study for my fame. The professor have no problem getting a grant, since Pluto is now well known to be interesting.
      The study show the mission can be done, but is still a paper tiger. Some studies suggest fusion power propulsion.
      Pluto is the choice for the study with the big interest for the world.
      But too much risk with untested and very expensive equipment.

      Now landers on Europa and Pluto will be even more risky, there might be penitente structures on the surface.

      • Charley October 13, 2018, 17:57

        Now Andrei – let’s start getting into the nitty-gritty concerning the statement that you made above about the following:
        “The study show the mission can be done, but is still a paper tiger. Some studies suggest fusion power propulsion.”
        Now, I did look at the paper, but let’s be honest about all these particular papers that are put out there-they are as dense as can be and would require considerable careful reading to extract what they’re trying to say.
        That being said, I did look over the paper and I’m being led to believe that they’re talking about a fusion engine that can be ignited by (I assume) some type of electron or heavy Ion directed beam to initiate ignition with the fusion fuel. This seems highly problematical (at first glance) as we are having trouble here human on earth attempting to perform inertial fusion in a controlled environment. Am I getting the proper gist of the paper?

  • Patient Observer October 8, 2018, 18:57

    One thing KiloPower could do is power an ion engine to reduce these ridiculously long mission times that are now reliant on multiple planetary flybys. I, for one, do not have the patience or that many years left for a 10-15 year mission.

    • Daniel Högberg October 9, 2018, 4:16


    • Antonio October 9, 2018, 15:43

      Better restart development of NERVA. KiloPower simply will not change d-V too much. I mean, scientific payload would be low, it would take eons to reach Pluto and it would have no capability to orbit Pluto.

    • Charley October 9, 2018, 18:37

      Patient Observer, while I have no numbers concerning your observations of an ion engine, it becomes a little difficult to give a quantitative figure as to how much time saving such propulsion provides. If you want to achieve orbit, you got to accelerate, cruise, and de-accelerate-perhaps with a gravity assist capture to get your orbit. But I don’t know what the numbers would be our whether the savings would be great. Do you happen to have any numbers?
      If memory serves me the Isp is in the 10,000-30,000 range. But the thrust is not significant.

      • Patient Observer October 9, 2018, 21:29

        Ideally, Earth escape velocity would be achieved using chemical rockets (perhaps the SLS or similar) with ion engines for the long haul. Dawn, which orbited Vesta and in currently orbiting Ceres, used ion engines to good effect. Per Wikipedia:

        Dawn can perform a velocity change of more than 10 km/s over the course of its mission, far more than any previous spacecraft achieved with onboard propellant after separation from its launch rocket.[46] However, the thrust is very gentle; it would take four days at full throttle to accelerate Dawn from zero to sixty miles per hour (96 km / hour).[7]

        Based on the foregoing, a ∆V of 11,000 mph could be achieved in two years. I would hope perhaps twice that acceleration could be achieved resulting in a ∆V of 22,000 mph over two years. Of course mass ratio and specific impulse would need to be at appropriate values. There is a huge library of information on various interplanetary propulsion schemes, monograms and calculations at the following link but be prepared by clearing your appointment calendar:


      • Andrei October 10, 2018, 9:45

        Charely, yes an ion engine can shorten flight time somewhat but have very little thrust, a few Newtons.
        So you are right the flight will be like with Dawn, and a slow catch up approach.
        The best experiment ion engine provide 5N, but require 100kW of power = thirteen 8 kW Kilopower units to be bolted to the spacecraft.

        A mission to Chiron have been compared for 2 kinds of propulsion.
        (Yes Chiron not Karon/Charon of Pluto, the enigmatic small world with a ring between Uranus and Saturn that sometimes have CO and cyanid atmosphere – or is it very huge comet?)

        Missions have the same 13 years to reach Chiron with 1 year of observations for the two alternatives.

        In a Radioisotope Electric Propulsion craft the reactor weights 186 kg, need 6 kg of radioactive material, and 450 kg Xenon for a total probe mass of 1300 kilos.
        (This probe is lighter from the start it get extra boost benefit from upper stage. Same launcher is proposed for both.)

        Nuclear Electric Propulsion will need 1142 kg reactor loaded with 75 kg of nuclear material, 3 ion engines of 7000W that use 1600 kg of Xenon for the same mission. Total weight 4 tons.

        The cost is not calculated but I think the NEP cost a lot more than the smaller craft with Hall element thrusters. REP is much more radioactive but it does no difference in unmanned probes.

        (With 75 kg of nuclear material in the NEP alternative, there’s one more option Nuclear Thermal Rocket.
        Yes this is very speculative, even so when using so much radioactive material as 75 kilos it make much more sense with a NTR that I made one ‘back of envelope’ calculation for.
        It appear quite faster as it reach cruise speed very fast and breaks efficient at the goal so it cut the transit time by half or more. Simple as more reaction mass mean shorter mission with NTR, minus the extra mass.
        But neither Bimodal Nuclear Thermal Rocket or Nuclear lightbulb is in development. Still I feel it would be a waste not to consider this alternative.)

        • Charley October 10, 2018, 17:28

          “ion engine provide 5N, but require 100kW…3 ion engines of 7000W …”
          Wow, a lot of wasted energy here…

          • Andrei October 12, 2018, 12:00

            Yes it is a lot of waste.
            Some energy go lost in conversion/power production and a lot of heat is waste heat from the fast reactor or the six 150W ASRG.
            It started to seem more logic to go for a more direct way of providing thrust. Where the reaction mass is heated directly by the atomic material.
            And btw: The most powerful Hall unit take 5kW for a meager 0,5 N of thrust. To compare with the above.

  • Nate October 8, 2018, 19:23

    What are the odds that so-called Planet X will be discovered in time and within the range of New Horizon’s trajectory? I would guess pretty slim odds!

    • Antonio October 9, 2018, 15:45

      Zero. If it were that near, it would have already been found.

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