Mission: Hayabusa 2 Options

[Marcin600]

2019-08-22 Hayabusa2 reporter briefing in English :

- Place names related to the artificial crater
- Status of MINERVA-II1
- Future plans
- Capsule re-entry sequence and recovery method

About MINERVA-II2:
„In order to obtain meaningful results using Rover-2 (university consortium development), separation from a relatively high altitude (about 1km) is planned, with the descent to the asteroid surface over time used to estimate the asteroid’s gravitational field by monitoring the descending orbit”.

• September 5 - „the target marker separation operation will be performed as a rehearsal for MINERVA-II2 separation. The two target markers will be separated at an altitude of about 1km”
• September 24 (planned) - details of this operation will be explained at the press briefing
• Nov-Dec 2019 - departure from Ryugu;
• end of 2020 - capsule re-entry


Omusubi-Kororin crater: "...The crater will also continue to be referred to as the “SCI crater”, depending on the situation..."


(Image credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagoya University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST. I added new boulder names and scale bar)

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[Marcin600]

And from previous press material (July 25) - photo of SCI crater (Omusubi-Kororin) from above the Ryugu surface
(Oryginal picture from the Hayabusa2 website. Credit:JAXA, modificated)

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[Marcin600]

My attempt to link both views of the SCI crater (oryginal pictures from the Hayabusa2 website: 1 and 2 . Credit:JAXA, modificated ):

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[Marcin600]

New names of boulders inside SCI crater (Oryginal picture on the Hayabusa2 website. Credit:JAXA, modificated)

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[Marcin600]

September 3: "...On August 29, the back-up reaction wheel that has not been used since October last year was tested, and an abnormal value (an increased torque) was detected. The spacecraft therefore autonomously moved into the Safe-Hold state. ... On August 30...the spacecraft returned to normal [state]. However, as the spacecraft moved away from the home position due to entering Safe-Hold, we are currently having to return to the home position..."

September 6 [Google translation]: "Hayabusa 2" was away from the home position (HP), but now it has returned to almost HP. It was planned to arrive at HP this weekend, but given the possibility of approaching Typhoon No. 15 and affecting the operation of ground stations on Sunday and Monday, HP will arrive on Tuesday (9/10). [We] adjusted the speed of the spacecraft."

September 3 (again): "...The ’Target marker separation operation’ scheduled for September 5 has been postponed due to the spacecraft entering the Safe-Hold state...We will report again about the target marker separation when a new schedule has been decided."

[Marcin600]

„Image of the first target marker (TM-E) separation”.
„This is an overlay of images taken every 4s (for ~1min) as the spacecraft ascends at 11cm/s. TM descent speed is still almost zero. Separation time: 2019/9/17 at 01:17 JST. Altitude: 1km.”

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[Marcin600]

„The separation image of the 2nd target marker, TM-C.”
„This is an overlay of images taken every 4s (for ~1min) while the spacecraft ascends at 11cm/s. TM descent speed is still almost zero. Separation time: 2019/9/17 at 01:24 JST. Altitude: 1km.”

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[OrbitrapInSpace]

From Jaxa twitter :

[MINERVA-II2] Today (09/28) at 10:30 JST (on-board time), the spacecraft began its descent from the home position for the separation operation of MINERVA-II2 (Rover2).

[Explorer1]

Was there ever any follow-up on whether they restored functionality, or what the original problem was? Is it just a brick being dropped off before departure, or can we expect data (and images)?

[Phil Stooke]

It's not functioning. I think it is being dropped to monitor its motion as a probe of gravity.

Phil

[Marcin600]

A press conference on Minerva-II2 was held on September 24 - pdf materials (in Japanese only) are: here and here

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[Marcin600]

Terribly coarse Google translation - I am very sorry for that - but reflecting the sense of the current situation of the lander:


MINERVA-II2: separation from 1 km - October 3, 0:00~2:00 JST; impact - October 8 (JST)

MINERVA-II2 - Current status and purpose of separation operation:

- In the operation check on the machine, although communication can be established between Hayabusa 2 and MINERVA-II2, the MINERVA-II2 data processing system cannot be started normally. This situation is still the same
- In order to achieve scientific results in the MINERVA-II2 separation operation, the Hayabusa 2 team, the US University of Colorado, Kyushu Institute of Technology, and Tohoku University were examined.
- The aim is to separate the MINERVA-II2 at a slightly higher altitude and make the Ryugu go around several times instead of moving the surface and imaging after the landing. If we can observe the orbital motion from Hayabusa 2, we can expect to know more about Ryugu's gravitational field.

Significance of MINERVA-II2 separation / round operation:
- Acquire scientific data that contributes to improving the accuracy of Ryugu's gravity model
- Accumulate orbiting technology by orbiting small artifacts on asteroids

Separation / round operation plan:
- Separated for the surface of Ryugu at an altitude of about 1km
- Separation from the equator toward Ryugu rotation direction
- Attempt optical imaging of the motion after separation using ONC-W1 & W2 and ONC-T

Predicted value for throwing trajectory:
- Orbit type-Equatorial orbit
- Orbit life (predicted)-about 5 days (± several days)
- Number of laps (forecast)-about 8 times (± several times)
- Period (first period) (prediction)-about 17 hours (± several hours)

MINERVA-II2 Ryugu grounding and subsequent operation:
- The ground contact speed of Rover 2 is about 0.5 m / s. This is the same level as dropping from a height of about 1.5 cm on the ground. The rover is caused by a grounding impact.
- Less likely to break
- It is the original experimental item of MINERVA-II2-Micro-hop movement by eccentric motor (Tohoku Univ.) - Elastic reaction reaction movement using leaf spring (Osaka Univ.)-Play force reaction movement using permanent magnet (Tokyo Denki University)
- MICAM camera (Tokyo University of Science) cannot be implemented unless the data processing system is restored.
- As for the recoil movement mechanism using bimetal (Yamagata University), the rover may move due to temperature changes due to sunshine and shade on Ryugu. However, it is difficult to check the status of movement

[Marcin600]

In short, as Phil wrote: they will drop it from a 1 km and watch how it orbits the asteroid and lands after a few days - studying the gravitational field.

If nothing changes (they won't be able to restart Minerva's systems) - no photos from the lander should be expected. Only photos of Minerva in space and possibly on the surface of Ryugu. Maybe also a little hops on the surface (jumping brick)

[Marcin600]

From JAXA Twitter:
"MINERVA-II2 is confirmed to have separated today (10/3) at 01:38 JST. The separation time was 00:57 JST (on-board time). The spacecraft condition is normal."
"This is MINERVA-II2 captured by the wide-angle optical navigation camera (ONC-W2) immediately after separation. Radio-waves are also being received from MINERVA-II2. (Credit: JAXA, Chiba Institute of Technology & collaborators)"
"...the operation is ongoing! In the future, we will observe the orbital motion of MINERVA-II2 after its separation."

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[Marcin600]

On November 5-7, 2019 took place a meeting - workshop "Asteroid Science in the Age of Hayabusa2 and OSIRIS-REx". The workshop website has a collection of interesting abstracts (pdf’s) about scientific results from Ryugu and Bennu, containing article about the artificial SCI crater on Ryugu


Some new data from this article [text highlights are mine, the picture - Figure 1 - comes from the cited article]:

SPACE IMPACT EXPERIMENT ON RYUGU: ARTIFICIAL CRATER. T. Kadono et al. Asteroid Science 2019 (LPI Contrib. No. 2189)

„...This image was taken by ONC-T in the low-altitude operation at 1.7 km altitude... A crater rim also appeared as a part of a semicircle in the image. The estimated location of the crater rim is shown as a dashed curve. The deposition rim is a strong evidence for the crater formation occurring in the gravity-dominated regime.

The diameter from a point on the rim to an opposite Drim was ~15 m. Using an empirical equation D = Drim/1.3, where D is the crater diameter at an initial surface elevation [9], we determine the crater radius of the SCI crater R = D/2 to be 6.5 m.

We calculate the SCI crater radius using the conventional π scaling law applied for a typical sand surface [9]. We find that the SCI impact crater is about 5% smaller than that calculated for sand. In spite of the difference, it should be formed on a cohesionless surface such as one made of sand, because even a small amount of cohesion limits the crater growth in this microgravity environment and prohibits the crater diameter to be larger than 10 m. Thus, we can reasonably conclude that the surface of Ryugu is composed of sand-like cohesionless materials.

We found a pit close to the impact point on the crater floor (an arrow in Fig. 1). The pit entrance is at a depth of 1.7 m from the initial surface; the diameter and the depth of the pit is >2 m and 0.6 m, respectively. The pit has a conical shape similar to a simple crater in laboratory experiments [8]. The pit might result from the SCI impact on a subsurface layer with a cohesion strength. The cohesion strength of the subsurface layer is estimated by the dynamic pressure generated on the layer, which is caused by the material flow with the particle velocity. We calculated this pressure from the Maxwell’s Z-model [9]. Assuming the typical z value of 3 for granular materials, R = 6.5 m, a non-cohesive upper layer with a thickness of 1.7 m, and a pit diameter of 2 m formed on a cohesive subsurface layer, the dynamic pressure can be obtained as about 300 Pa at the center of the pit and about 130 Pa at the rim of the pit. Thus, the cohesion strength of the subsurface layer is speculated to be smaller than about 300 Pa and larger than about 130 Pa...”

[8] Melosh H. J. (1989) Impact cratering: A geologic process.
[9] Housen K. R. and Holsapple K. A. (2011) Icarus, 211, 856-875.

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