New Horizons: Pre-launch, launch and main cruise, Pluto and the Kuiper belt Options

[Alan Stern]

Interesting, thanks. Is that simulated RTG not useful for spin balance testing? And was that simulator an active heat and electrical generating system minus the Pu?

The thermal/electrical simulator has no radioactive material. It doesn't match the
mass properties at all.

-Alan Stern

[RNeuhaus]

What is the purpose of the balancing test? In the space has no gravity and the balance of weight is of no matter or not?

As it is performing, I see that the weight balance is of vital importance and would like to understand its implications to the navigation control during the space cruise.

Whenever the spacecraft is in the space, does it matter the stability of route toward Pluton?

Does the balancing of rotation stability of spacecraft is like to balance a new tire?

Rodolfo

[Alan Stern]

What is the purpose of the balancing test? In the space has no gravity and the balance of weight is of no matter or not?

As it is performing, I see that the weight balance is of vital importance and would like to understand its implications to the navigation control during the space cruise.

Whenever the spacecraft is in the space, does it matter the stability of route toward Pluton?

Does the balancing of rotation stability of spacecraft is like to balance a new tire?

Rodolfo

It has nothing to do with the trajectory.

During the final phase of launch and most of the flight to Pluto, NH is spinning
endlessly like a top in order to simplify operations and reduce the amount of fuel
needed for pointing. The s/c has to be balanced for the spin to be stable and
without any excessive nutation. Thus the need to do the spin balance testing.
This was done back in Maryland and then again for a final check at the Cape
with the spacecraft fully configured for launch.

[dvandorn]

Ah, the old misunderstanding -- if there's no gravity in space, why worry about mass distribution?

Just because you're in a microgravity environment does not mean that mass goes away. Mass is a constant -- a kilogram of mass is a kilogram of mass, whether it's on Earth and weighs a kilogram or its in deep space and "weighs" nothing. (And no, I'm not inviting discussion of far-end-of-the-bell-curve theories about mass itself changing based on its distance from other large masses.)

Mass works the same way in space as it does on Earth, too -- it takes the same amount of force to overcome inertia in a microgravity environment as it does deep within a gravity field. So, balance is ultimately the same wherever you are, and it's just as important to know the mass balance on a spacecraft as it is on any piece of machinery you're going to be moving.

I hate to admit, I'm unsure whether New Horizons is planned to be spin-stabilized or three-axis stabilized. If it's to be spin-stabilized (which I'm thinking it is), then the mass balancing is even more important. It's exactly like the tire example you mentioned -- if there's a mass imbalance in a spinning object, the object will begin to wobble, and the wobble will reinforce itself until the object flies apart or until other motions couple into the wobble and the thing goes entirely out of control.

But even for three-axis-stabilized craft, you need to know your mass distribution very accurately, so you can place your thrusters in the right places, and fire them properly, to achieve both attitude and translation changes. Especially when you translate (i.e., change your overall path and speed), you have to thrust through your center of mass, and so you need to know your center of mass pretty accurately.

-the other Doug

[dvandorn]

That's what I get for taking 15 minutes to write and edit my post -- Alan got in ahead of me.

Yeah, I thought NH was to be spin-stabilized for most of its flight, I was just not completely sure. Thanks for the confirmation, Alan!

-the other Doug

[RNeuhaus]

Good explanations. I was able to grasp them.

I tought the spin had the purpose to distribute uniformly the heat, cool and solar radiation and cosmic as I have learned it from others spacescrafts which orbit around the Earth and also to Moon and Mars.

As the spacecraft is going farther from the sun, the spin for this space might be less importance every time it is moving further away. Now I realice that the spin helps the spacecraft to avoid any wobbing during its trajectory and also to helps to manage better the thrusters after knowing the mass' properties of NH.

Well, as I see it, NH will be spinning on all way toward the Pluto. It would become an even more complicated to control the pointing of any navigation instrument to stars, to photograph any images on planets when the spacecraft is spinning.

Then maybe, before to take any picture, or any measurement, one of three (x-y-z?) reaction wheels will be activated to stop before conducting any science activities when it is flying-by to any celestial bodies (Jupiter, Galliean Moons, Saturn?, Uranus, Neptune and Pluto and its three moons).

Here, I have an inquietant question. It is related to reaction wheels as it is one of the most delicate since it has short Meant Time Between Failures. Will the NH have enough redundancies to cover all NH's lifetime trip to Pluto. I am thinking that the spinning factor will help to NH to avoid the use as less as possible the wheel reactions or not?

Rodolfo

[BPCooper]

The thermal/electrical simulator has no radioactive material. It doesn't match the
mass properties at all.

Despite not having the Pu, as I know, I would have figured it was designed to have the same mass/weight while still providing power using electricity.

[john_s]

Then maybe, before to take any picture, or any measurement, one of three (x-y-z?) reaction wheels will be activated to stop before conducting any science activities when it is flying-by to any celestial bodies (Jupiter, Galliean Moons, Saturn?, Uranus, Neptune and Pluto and its three moons).

Here, I have an inquietant question. It is related to reaction wheels as it is one of the most delicate since it has short Meant Time Between Failures. Will the NH have enough redundancies to cover all NH's lifetime trip to Pluto. I am thinking that the spinning factor will help to NH to avoid the use as less as possible the wheel reactions or not?

Rodolfo

That's correct, we stop the spin when we want to make observations. However we do not carry reaction wheels- instead we use thrusters for controlling the spacecraft orientation and spin. This saves us mass compared to using reaction wheels, and eliminates a moving part that might fail, as you say. However it means that we have to be conservative in our maneuvering, because we have only a limited fuel supply. So spin mode helps us save fuel.

[BPCooper]

Spin test Monday:

http://www-pao.ksc.nasa.gov/kscpao/images/.../05pd2498-m.jpg

[Alan Stern]

New Horizons highlights for the week ending 11/18/05 include:

* Conducted Autonomy Review on 11/15
* Conducted Pre-Fueling Review on 11/16
* On basis of the above, decided to delay hydrazine fueling by six days to allow
for additional autonomy testing on the spacecraft and NHOPS.
* Observatory hydrazine fueling now scheduled for Sunday, 12/4. No change
to beginning of launch window; holding firm at 1/11/06.
* Completed dry spin balance on 11/17. No surprises.
* MSIM 4 Part 3 repeat for pactice began 11/17 and is scheduled to complete 11/19.

[Rakhir]

New Horizons Launch Preparations Move Ahead
http://pluto.jhuapl.edu/news_center/news/111805.htm

"Rocket motor set to boost NH toward Pluto will be delivered safely and within the rigorous engineering standards demanded in the assembly and testing of such hardware.

Boeing replaced the five striking workers with six non-striking workers; the extra assembly worker was added to provide additional oversight. Each of the six current workers has at least eight years of experience with Boeing upper stage motors and is fully qualified to work on the project.

"We expect this experienced team to finish processing the rocket motor on schedule, so New Horizons can meet its prime launch opportunity in January."

[Comga]

Despite not having the Pu, as I know, I would have figured it was designed to have the same mass/weight while still providing power using electricity.

If you need to confirm what Alan says, look at the image from BPCoooper in

http://www.unmannedspaceflight.com/index.p...=27817&st=285&#

You will see the dummy RTG on the floor during the spin test. The blur of the RTG mass simulator is metalic gray, without heat fins. Obviously a completely different piece of hardware. Perhaps trying to get the power, mass, CG, and all other parameters equal to the real RTG was more complex than just building two simpler devices, one for temporary power, one for the spin tests.

[Decepticon]

I have a question that has been asked of me before but I really had no answer to.


Are Pluto and Charon close enough to cause tidal heating?
Could Pluto's core be warm?

[john_s]

I have a question that has been asked of me before but I really had no answer to.
Are Pluto and Charon close enough to cause tidal heating?
Could Pluto's core be warm?

They are certainly close enough, but closeness isn't the only requirement. For one body to cause tidal heating in another, the relative distance and/or orientation of the two bodies must change, so that there's some periodic change in the shape of the body being heated- it's the changing shape that causes the heating. Pluto and Charon are locked into almost perfectly circular orbits around their center of mass, so while each is creating a large bulge in the surface of the other, the bulge never changes shape, so there's probably no significant tidal heating.

Pluto's core might still be warm, but it would be from radioactive heat in its interior, not from heating by Charon.

[tasp]

I have a question that has been asked of me before but I really had no answer to.
Are Pluto and Charon close enough to cause tidal heating?
Could Pluto's core be warm?

Assuming Pluto and Charon did not form tide locked (probably a pretty good bet), they would have interacted tidally till they did achieve lock.

Dissipation of significant amounts of heat in either body, considering their composition, would have been very interesting.

Consider that we know Charon's surface is depleted in methane compared to Pluto. Considering the volatility of methane, we may have some evidence of a past period of significant tidal heating on Charon.

Perhaps the NH mission will photograph signs of past heating on Charon.