Adv. SpaceRet. Vol. 10. No. 3—4. pp. (3)341—(3)342, 1990 0273-1177/90S0.00 + .50Printedin Great Britain. All rights reserved. Copyright © 1989 COSPAR

FUTURE PLANETARY MISSIONSIN JAPAN

JunNishimuraThe Institute ofSpaceandAstronauticalScience,Yoshino-dai3—1—i, Sagamihara,Kanagawa,Japan

Space science program in Japan has been organized by the Institute ofSpace and Astronautical Science (ISAS). The institute has conducted thespace programs of Astrophysics, Solar Terrestial Physics, Earth Science andPlanetary science. On the other hand, space application program has beenconducted by the National Space Development Agency of Japan (NASDA). Eachprogram for Space Science and Application has been proposed by each agency,and the programs are discussed and coherently organized as a whole by theSpace Activity Commissions which belong to the Prime Ministers Office.

ISAS is a joint institute of inter-university, and has been organizedby the academic circle. The institute has been spending much efforts todevelop scientific satellites, satellite launchers, sounding rockets andsystems of balloons for scientific observations. The institute has conductedprograms of almost one small/moderate size satellite, 5 to 6 soundingrockets and 10 to 15 balloons per year. The most recent ISAS satellitelauncher is M3S-II, which is capable to send a 770 kg satellite to the lowearth orbit (250 km).

The strategy of ISAS satellites is to put the importance of theintellectual continuity in each discipline and to respond quickly to thecurrent status of the space science. Then we need to keep the appropriatefrequency of the satellites. To keep the frequency and to performefficiently, the satellites are smell/moderate size with ISAS tran~ortationsystems, hut the missions must focus on the subjects and be well defined. Haalso needs to have similar strategy for the ISAS planetary missions.

As the planetary missions, cia have performed Halley missions, Sakigakeand Suisci, in 1985. We now schedule to launch a Lunar Swing-by Mission,MUSES-A, early in 1989. We are now planning future planetary missions byproviding up-graded ISAS transportation systems, which has a few timescapable to the current M3S-II launcher. We could send a space probe of massof 300-400 kg to the Moon or Venus using this up-graded launcher. Then ISASdomestic missions is the nature of precursor, reconnaissance and 3houldfocus on few subjects. We also plan a few large-scale missions as a nationalor international programs, in which the missions are for comprehensive andoverall exploration. For the national programs in this case, we would useHil rockets now under development by NASDA.

ISAS is now discussion the model missions, which will be realized inrnid-1990’s with ISAS up-graded transportation systems. The discussions areconcentrated on the missions of Lunar, Venus and Comet Fly-by and samplereturn. ISAS is also discussing on the possibility of Mars and Mercurymissions, but they are now still in a preliminary stage. For the futureISAS missions, we put first priority to the Space VLSI mission (VSOP) to belaunched in 1994. For the planetary missions, ISAS did not yet discuss thepriority for each mission. More details of those missions and the prioritiesfor those missions will be discussed taking further one year.

Here, I briefly describe those missions now under investigaticis.

1 . Lunar missionsThe program is to concentrate to the seismological study of the Moon.

An eccentric polar orbit is used to deploy three penetrators, each 70 kg, onthe lunar surface with an impact velocity of about 250 rn/s. Each penetratorcontains two seismometers and a heat-flow probe. The network consisting of

(3)34 1

(3)342 J. Nishimura

three seismic stet~ons ~1ms to detectse1sm~c waves from deep moonquekessources which are located relat~velvaccurately by the Apollo seismicnetwork and to clarify a long-standingq.~estion of t-e existence o~ the lunarcore. The hear-flow probe will provimekey data for better understanding theglobal average of the lunar heat flow.The data from the penetrators will betransmitted to the earth via theremote sensing polar orbitingspacecraft. The altitude of thisspacecraft will be 100 kg. The remotesensing will focus to few observationsusing the soectrometers of visible,infrared, X-rays and a Gamma-rays.This will exolore the global namoing ~ ..‘ 0

of mineralogical and elemental a

composition of the moon. The ~ ~ ~

instruments of high resolution and ~high sensitivity are now underinvestigation. Fig. 1 Concept of Penetrator

2. Venus mission.Since the Venus has no intrinsic

magnetic field, the solar windinteract directly with the Veriusianatmosphere. Thus the study of thedirect interaction of the solar windwith Venusian atmosphere will help us .?~

greatly to understand dynamics in theterrastial magnetosphere and atmo- ~sphere. The plan is to put a space- .~ ~

orbit of 30,000kmx 300 km. Scientific _____ 1/IfU~ images for D/M ______________

Hydrogen ratio ) measurements areplanned to obtain various kinds of _______________

data on Venus plasma and atmosphere. -.

Besides these observations, Venusballoons at an altitude of 20 km orless are under investigation to a

observe the dynamic flow of the Venusatmosphere at this altitude and to Fig. 2 Venus Missionstudy directly the Venus atmosphericphenomena and its constituents.

3. Comet Sample Return MissionAn ambitious mission for

collecting dusts in comet coma andreturning them to the earth is being .~..

planned in ISAS in collaborating with ~ ..

NASA In this mission direct imaging ..~ / ~ ~

of comet nucleus is also consideredMost nearest chance for this mission / ~is to launch a soace craft in October ~-. ~.

1996, approach Comet Wirtanen in March1997, and returns to the earth in ~October 2000. When it returns to theearth, the spacecraft is decceleratedusing aerodynamic brake and finallycaotured by NASA’s OMV ( OrbitalManeuvering Vehicle ). The space craft -

approaches to the comet with a . 0relative velocity of less than 10kn/s, so that we hope we can obtainintact dust particles in the coma bya dust collector which is now under Fig. 3 Sarr~le ~erurn Missiondevelopment in ISAS and NASA. -