Trajectory Profile

March 29, 2010

Hayabusa has been propelled, and it successfully traversed from day side to night side, having flown over the south pole, having avoided collision to the Earth.
On 27th of this month, Hayabusa completed its long ion engine propulsion from last spring, and it stopped the ion engine on the day.

The impact parameter on BR-BT plane, when converted, says the instantaneous closest distance now is about 20 thousand kilometers from the center of Earth.
What is left is a series of trajectory corrections, and the project team is finalizing the preparations for them.

March 23, 2010

Ion engines aboard Hayabusa have worked well.
21st Monday is a national holiday in Japan and this status update becomes late.

From this week, the orbit information is shown in magnified figures as below. They may need some explanation.
When the reentry capsule is made plunge into atmosphere, it must fly in the direction compliant with the Earth rotation direction so that the entry speed can be lowered. It means the incoming trajectory needs to approach from the night of the Earth, while current approach is from the day side of the Earth. And the trajectory must traverse to the opposite side from present flight path. The resulted outgoing path after the virtual swingby will leave Earth in opposite direction when this traverse completes.

When move to the other side, an unintended interruption of the ion engine propulsion has to be taken into account and even an instantaneous trajectory shall not run cross the Earth disk. And the sophisticated orbit maneuver is devised to fly over the Antarctica on the way.

The continuous ion engine propulsion lasts until the end of March, when Hayabusa will be guided to a tentative target point with respect to the Earth. It is intentionally set very far from the Earth taking the enough guidance error into account, when Hayabusa reaches the point avoiding inadvertent entry to the atmosphere.

Hayabusa's attitude controllability is well operable, but the orbit correction direction is not arbitrary and restricted. Hayabusa is awkward in exhibiting thrust in Sun or anti-Sun direction. In order that the orbit correction can be performed mostly in the tangential direction to the orbital motion around the Sun in a series of orbit corrections from April, the target point should be tactically prescribed and defined.

As of March 20th, an instantaneous closest distance to Earth this June will be 46 thousand kilometers. Hayabusa soon reaches the orbit that passes through within a geosynchronous orbit.

March 12, 2010

From last week to this week, a precise orbit determination has been performed and the closest distance was not improved much. The current closest distance to Earth is about 130 thousand kilometers.
The figure attached tells the outbound trajectory from Earth veers off showing the swingby characteristics.
From now on, the ion engines are operated to target the prescribed point around the Earth, and the decreasing speed for the closest distance will be decelerated.

March 5, 2010

Hayabusa is now on the orbit passing within the half of the Moon's distance, at 160 thousand kilometers. From March 5th, the ion engines aboard will stop and the high precision orbit estimation is performed.
From now on, not only the distance but also the approach direction are going to be tuned.

March 1, 2010

Hayabusa has reached the orbit that will pass through within the Moon's distance this June. The closest distance from the Earth will be 310 thousand kilometers.
Hayabusa will stop the engine briefly at the beginning of March to conduct a precise orbit estimation for the subsequent flight. The ion engines aboard are functioning normally.

February 18, 2010

This week, the estimated orbit concluded that the Hayabusa would be on the path skimming the Moon orbit this June. The closest approach distance from the Earth is found 470 thousand kilometers, just above the Moon's orbit. Now the goal for reentry has loomed eventually.

February 15, 2010

Hayabusa has kept the approach path right on the course targeted to the Earth. The closest approach to the Earth is 600 thousand kilometers as of today. And in a few weeks, Hayabusa will be on the trajectory passing through within the Moon's distance. The ion engines aboard have worked normally last week.

The distance between the spacecraft and the Sun is gradually decreasing to 1AU that is the revolution radius of the Earth. The temperature measured at various points on the spacecraft increases gradually, and the project team has started to tackle with the heater control to prevent over-heating. The radio communication time is now only two minutes each way with enhanced bit rate.

February 9, 2010

I was confirmed that Hayabusa has reached the trajectory that will pass at 750 thousand kilometers from Earth. It is two times as distant as to the Moon. Ion engines aboard have worked well since last week, and the spacecraft almost precisely has been guided along the target line shown. Around at the end of this month, Hayabusa will be on the orbit that passes through even within Moon's distance.

February 1, 2010

It was confirmed that the closest approach distance this June will be within 1 million kilometers. Every week the ion engine aboard the spacecraft reduces the distance 150 thousand kilometers per week. It is 2.5 times as far as that to the moon. In about a month, the distance will become shorter than that to the moon. Currently, the spacecraft is at 1.3 Astronautical Unit (AU) from the Sun and at 0.3 AU from the Earth.

Project manager Junichiro Kawaguchi

January 21, 2010

The orbit determination this week indicates the closest approach distance to Earth is now around 1.15 million kilometers, which is about three times as distant as that to the Moon. The burn time left for ion engines aboard is two months.

While the figures show how the Hayabusa mother ship returns back to Earth, the project team is struggling to have the Reentry Capsule recovery on the gerund with much more accurate navigation and guidance.

January 14, 2010

Hayabusa this week has further narrowed the closest approach distance to Earth, and the distance has become down to about 1.4 million kilometers. The out-of-plane approach direction is also on the exact path planned as the figures indicate. The fact that the spacecraft is on the path passing through the Earth gravity sphere does mean that Hayabusa has accomplished its round-trip cruise from Earth, by way of Itokawa and back to Earth.
Hayabusa is now the world's first spacecraft returning back to Earth after landing and lifting off the surface of a celestial object outside Earth-Moon system.
The project plans to make it fly within Moon's distance next, and reentry into Earth atmosphere, and recovery of the capsule on the ground. It is currently at around 60 million kilometers from Earth with additional ion engine propulsion for two months.

January 6, 2010

The orbital information was updated on January 6th, since Hayabusa restarted its ion engine propulsion last week. The instantaneous closest approach distance has now got down to 1.6 million kilometer from Earth, which is almost that of the boundary of Earth gravity sphere. The radius of the sphere is not definite, and depending on various views, the radius is differently and alternatively defined. However, what we call Hill's sphere is conceived an objective indicator as Earth gravity sphere, since the Lagrange points L1 and L2 are theoretically on the sphere boundary. The distance is 1.5 million kilometer.

Next week, when the next updated orbit information is obtained, the project team can clearly state that Hayabusa is now on the path passing through the Earth gravity sphere, which means the project will have succeeded in having guided Hayabusa spacecraft back home.

* Note even though the path passes through Earth gravity sphere, it does not mean Hayabusa is spontaneously captured by Earth.

January 4, 2010

Hayabusa had performed the ion engine cruise by December 27th, when it stopped the propulsion until January 1st in order that the precise orbit determination was to be conducted. The task designated as Orbit Determination was participated not only by JAXA antenna but also by NASA Deep Space Network (DSN) antenna which provided the Delta-VLBI (Very Long Baseline Interferometry) measurements gathering the accurate information as to position and velocity of the spacecraft.
On January 1st, Hayabusa successfully restarted its ion engine again in a new combined mode that was established last November.
The distance to the Hayabusa from Earth has now been lower than 0.5 AU, and next week, the project team is sure to state that the Hayabusa is on a return path coming into the sphere of Earth's gravity.