Mission: Hayabusa 2 Options

[Paolo]

Ryugu seen from a distance of 2600km

[Phil Stooke]

"Ryugu is not symmetrical, is it? Top one third looks darker."

The important thing about this is that you can never trust the appearance of a pixel right on the edge of something. We have no way of telling how much of that pixel is covering Ryugu and how much is covering the black space around it. Usually people assume that you need at least 3 pixels across something to interpret it. In this case that would be 3 pixels across that dark-looking area (about 10 pixels across the asteroid). If it still looks dark then, we know it's dark!

Phil

[Guest_mcmcmc_*]

Press conference documentation in english:
http://www.hayabusa2.jaxa.jp/topics/press/...ss20180607e.pdf

[pandaneko]

Q&A continues.

Q. How do you approach Ryugu? My guess is that you first place Hayabusa 2 on the same planar orbit as Ryugu
and then slowly adjust the curvature. Is that right?

Since there is a mass difference speeding up of Hayabusa 2 in trying to catch up with Ryugu may lead to
overshooting. How can you make sure it will not happen?
June 03, 2018 - : 64 year old

A. We conducted an earth swing-by on 3 December 2015 and that was for Hayabusa 2 to move into the same
orbital plane as Ryugu.

After that over 2.5 years we fired ion engines on and off so that Hayabusa 2's orbit becomes closer to that of
Ryugu.

That is to say, we tried to enlarge Hayabusa 2 's orbit little by little. Here, the mass difference is irrelevant to
this operation.

We, however, need to take into account, pull by the Sun, and pull by other planets, in addition to the solar rays
pressure on Hayabusa 2.

In the final stage we need to take into account Ryugu's gravitational pull. That is why we will be conducting
a free fall to 1km height. Hayabusa 2's speed varies depending on where it is flying, maximum speed is
somethinglike 33km/s and slowest is 23km/s.

P

There will be more Q&As.

[pandaneko]

Q&A continues.

Q. Sampled materials are likely to be organic in origin. Do you store them in a fridge like place until they
reach Earth? June 03, 2018 - : 58 year old

A. There is no fridge in Hayabusa 2 capsule. It is assumed that the surface temp. on Hayabusa capsule reached
3,000 degrees C.

However, the temp. inside the capsule was kept at less than 100 degrees C. You may think that 100 degrees C
is too high, but the surface temp. on Itokawa was as high as 100, so, there was not much problem.

With Ryugu we think that the surface temp. will be similar, so there is no fridge. We can measure the surface
temp. of Ryugu accurately with the mid infra red camera.

P

[pandaneko]

Q&A

Q. There were many troubles with Hayabusa 1's flight. Have you had similar problems this time?
June 03, 2018 - : 19 year old

A. With Hayabusa 1 reaction wheels broke down. They control attitude. There were 3 of them on Hayabusa 1.
One broke before arriving, and another broke immediately after arrival. In addition, one of the four ione engines
on 1 was not in good health, right from the start.

With 2, there has not been any major problem, so far. There are 4 reaction wheels and all of them are healthy.
Also, all 4 of the ion engnines are healthy and mission continues according to original design.

P

There are a little more Qs and As. One thing I came to realise is that rather a lot of xenon
still left is perhaps for moving Hayabusa 2 to its eventual parking position, L2?, L3?, I do not remember,
but I do remember the parking issue JAXA talked about with Hayabusa 1 before they had to burn it
with adiabatic compression.

[Paolo]

there was a paper at the 2016 IAC Congress (paper no. IAC-16.C1.5.11) on Hayabusa 2 mission extension. four candidates for an NEA flyby have been identified, with the best being 630 m (172034) 2001 WR1, for a flyby on 27 June 2023

[pandaneko]

Accordning to the log I have been keeping all chemical thrusters, except #2, #4, and #8 have been
fired since 1 June.

P

[pandaneko]

Q&A continues. This is the last in the Q&A box, but JAXA seem to be accepting questions at any time and I may find some more
in due course.

Q. Do you have a plan to make a movie of touch down using an on-borad camera?
June 02, 2018 - : 21 year old

A. This monitor camera was made thanks to the donation from people like you. Therefore, if possible, we would like to make such a movie.

However, there will be all kinds of delicate operational issues during touch down and it is possible that we may not be able to do that,
but we will try our best.


P

[nprev]

A touchdown movie would be truly spectacular; hope they can manage it!

[pandaneko]

From the twitter portion of Hayabusa 2 main web page.

8 June 2018

First TCM01 during optical navigation was conducted. We fired thrusters several times during 12:30 to 13:40 on 8 June, and
accelerated Hayabusa 2 by 24cm/s in minus X, 5cm/s in minus Y, and 14cm/s in plus Z directions. Consequently, the relative distance
is now 1900km, velocity 2.35m/s

6 June

LIDAR was powered on after 2 year long crusing to check its health. We did it step by step, Each command response needs 32
minutes for confirmation. Altogether it took us 5 hours to complete this checking. We cannot use it yet as the distance is still too
large for the LIDAR.

P

[Guest_mcmcmc_*]

accelerated Hayabusa 2 by 24cm/s in minus X

Misleading translation? It looks like H2 actually slowed down:

https://aliveuniverse.today/rubriche/missio...proccio-a-ryugu

[Phil Stooke]

Probably a matter of frames of reference. The spacecraft needs to match speed with the asteroid in orbit around the Sun. Speeding up slightly in its orbit around the Sun might reduce its velocity with respect to Ryugu. I don't know the details, but that is most likely what is going on.

Phil

[pandaneko]

For clarification of the cordinate system I refer to page 16 of JAXA FACT sheet ver2.0, dated 19 April.

-X direction: where star tracker is pointing, as well as the re-entry capsule

-Y direction: where ONC-W2 is pointing, W2 is looking perpendicular to star tracker direction
+Y direction: where ion engines are pointing

+Z direction: is the direction of the earth because I can see two Ka band disk anntenae are pointing and it is opposit to
-Z direction: where sampler horn is pointing

My guess is that ONC-W2 is the donation camera.

P

[pandaneko]

Probably a matter of frames of reference. The spacecraft needs to match speed with the asteroid in orbit around the Sun. Speeding up slightly in its orbit around the Sun might reduce its velocity with respect to Ryugu. I don't know the details, but that is most likely what is going on.

Phil

This perhaps has something to do with my earlier translation about acceleration.

"We are at the very last stage of navigation and we are firing the ion engines into the acceleration direction.
Consequently, there are times when HY2 speed increases momentarily (conversely, meaning a longer orbital
period in the longer run, leading to a decreased flight velocity, which is a very interesting aspect of orbital
dynamics)

As a result, matching of HY2 orbit and that of Ryugu becomes better and the relative distance between them
decreases."

P