Ariane transfer vehicle in service of man in orbit

Acta Astronautica Vol. 19, No. 12, pp. 957-968, 1989 Printed in Great Britain.All rights reserved

0094-5765/89 $3.00+ 0.00 Copyright © 1989PergamonPress pie

ARIANE TRANSFER VEHICLE IN SERVICE OF MAN IN ORBITt N. DEUTSCHERand K. SCHEFOLD MBB/ERNO, Hiinefeldstrasse 1-5, D-2800 Bremen 1, F.R.G. and C. COUGNET MATRA, Z.I. du Palais, F-31400 Toulouse, France (Received 22 March 1989)

Abstract--The Ariane transfer vehicle (ATV), an Ariane 5 borne, unmanned propulsion vehicle, is designed to transport the logistics needed to resupply the International Space Station (ISS) and the man tended free flyer (MTFF) step 2 with pressurized and unpressurized cargo and to dispose the waste. The ATV is an expendable vehicle and is disposed of by a safe atmospheric burn up. In accordance with the AR5 schedule it should be operational in 1996 for missions toward ISS and beyond the year 2000 for MTFF 2 missions. The main constituents of the proposed ATV are the modified AR5 third stage L5, an upgraded VEB steering the launcher as well as the ATV and the P/L-adaptor providing mechanical and umbilical links to the payload. The mechanical part of the RVD-kit will be placed on the payload-module, the main RVD sensors are located on the adaptor and the needed computer intelligencewill be integrated on the VEB. To minimize the development, and recurring costs, the ATV concept fully complies to the idea of maximum use of existing hardware and software, mainly from the AR5, Hermes and Columbus programs thus minimizing development and recurring costs. The ATV is compatible to ISS, MTFF and OMV and is able to transport logistic modules compatible with NSTS and U.S.-expendable launchers.

I. I N T R O D U C T I O N

Leading to an operational Space Station, NASA, Japan, ESA and Canada are on the way to find their flight logistics system development to be pervasive to much of the Space Station. Existing Space Station logistics hardware design elements are driven by the yearly resupply and return requirements, the launch capacity of the launcher, the landing capability of the NSTS Orbiter, the average density of the supplies and products, the flight schedule during each flight, the inert weight of the elements as well as ground and orbiting processing of the supplies and products. The optimization of the systems capability to transport products and supplies through flight manifesting becomes an important point to tie all the parameters together. In this connection the development of an European cost-effective carrier being able to meet these Space Station return/resupply requirements comes into consideration, performing an alternative supplement to respective U.S. and Japanese concepts being developed. Using Ariane 5 as a launch vehicle, based on AR5 technologies, the development of the ATV could be carried through in parallel with the European launcher. Accommodation to standards and requirements ?Paper IAF-88-200 presented at the 39th Congress o f the International Astronautical Federation, Bangalore, India, 8-15 October 1988. A.A, 19112-..-C

prescribed by the Space Station is taken into consideration as well as the compatibility to OMV, NSTS and expendable U.S./Japanese launchers represents a main driver for the ATV development and concept. 2. ATV BASIC ASSUMPTIONS For definition, for setting up the requirements, for formulation of principle ideas and for development of the ATV some basic assumptions were specified: • The ATV is an AR5 borne, unmanned propulsion vehicle. • The ATV is a low cost vehicle and its definition should result from minimizing changes to the basic L5 and VEB. • The ATV baseline target is ISS and M T F F step 2 on a circular orbit (200--250 nm, e.g. 370-463 km of 28.5 ° inclination). • The ATV is launched by AR5 lower composite consisting of an H 155 core stage augmented by two P230 boosters. The launch site is CSG. (Centre Spatial Guyannaio). • For the baseline mission the ATV separation from AR5 will be in an 135 x 300 km transfer ellipse with i = 28.5 °. • The ATV is expendable and will be disposed of (including waste payloads) by a safe atmospheric burn up. e The ATV shall be operational in 1996 for ISS missions and beyond 2000 for M T F F 2 missions. 957

N. DEUTSCHERet al.

958 3. SAFETY

3.1. Safety requirements The probability that a mission will be successful depends strongly on the fulfilment of the safety requirements. In any case the ATV must meet the safety requirements of the ISS and the M T F F as well as the ESA System Safety Requirements (PSS-01-40). The ATV shall guarantee a safe retreat in case of failure. Therefore, the ATV functions used in proximity operations shall be at least fail safe and the ATV functions required for retreat shall be at least fail operational. On first failure the ATV must fly back to a safe point. The decision on retry depends on the reconfiguration or tests and/or possible support from the ISS. Furthermore, the ATV must provide override capabilities by man during operation in an automatic mode. No combination of two failures including S/W and operator errors shall result in catastrophic hazards. The ATV shall get monitoring and control from the Space Station when it is moved in ISS control zone. The compatibility of the ATV propulsion system with ISS must be guaranteed. Firing liquid propellant engines a safe distance from ISS/MTFF is necessary. Isolation capabilities must be provided. Finally, the generation of space debris in orbit must be avoided.

3.2. Safety principles In case of a first critical failure the ATV is still operational. This concerns the functions necessary for rendezvous, retreat and deorbitation. In case of a

second critical failure, the ATV is able to perform a safe retreat. In terms of mission, a decision to interrupt the mission after the first failure is accepted. Thus, a mission success probability of 99% is given. As a second failure must not endanger, in short or long term, the ISS, a safe withdraw mode is required.

4. ATV MISSION SEQUENCE The successive phases of the ATV during flight towards ISS are illustrated on Fig. 1. (1) Launch of the ATV will be by the AR5carrier from CSG. (2) After cut-off, the two P230-boosters, will be separated and parachuted towards the Atlantic Ocean. (3) The H155 stage will continue burning and the fairing will be separated during H155 boost. (4) After burn up of the second stage, the ATV will be separated and the H155 stage will return to Earth by safe re-entry/disposal. (5) The ATV is released into a transfer orbit of 135 × 300 km/28.5 ° inclination. (6) On this elliptical transfer orbit the ATV performs phase correction by free drift. The drift phase duration depends on the actual target orbit, i.e. 200-250 nm (370-463 km) and the initial phase difference. The maximum drift time for a 180 ° phasing is 27 h.

9 International Space Station

6

5

7t

8

Phasing ~

Separation H155/~,TV ~

~

-b-

flO SeparationISS

Proximity operations V Re-entry/

Fairing ~ separation ~ . / •/;<~.

2

C~ "---~<~:~ 4 2.Stage~ Re-entry/disposak~1

I P23O Separat,on

Launch f Y ~ P230 Recovery

Fig. 1. Global mission sequence.

disposal

Ariane transfer vehicle (7) During sequence phase (8) RAAN correction will be performed. RAAN correction manoeuvres are designed to correct max. 0.1 °. (8) From first drift orbit the ATV will arrive at a circular orbit 460 x 460 km by Hohmann transfer with intermediate 2.5 drift revolutions. Fine adjustment for transfer from 460 x 460 km orbit to a 470 km circular orbit will be performed by the SCA hydrazine system to the hold point 37 km behind the station. (9) The ATV will perform proximity and final approach manoeuvres and will be berthed to the ISS. (10) After separation from the target either passively by the OMV or actively via the ATV on-board cold-gas system, the ATV will drift into the departure zone of ISS. (11) The de-orbitation manoeuvre will be performed by one single burn of the main engine. Depending on the remaining propellants, a steeper re-entry angle can be achieved. The normal entry angle, a compromise between A V amount and debris impact area, is chosen to around 3° with a A V amount of 250m/s, resulting in an impact area length of 500 km. 5. D I S P O S A L

MODES

Of foremost interest with respect to safety considerations is the knowledge of the ATV debris scattered after the re-entry of the vehicle. Depending on the ballistic factor, the initial entry angle and the entry velocity, the individual fragments follow different trajectories as soon as they experience noticeable aerodynamic forces. The dependency of the length of the impact area on the entry angle for a return from a 460 km circular orbit is shown in Table 1: the steeper the entry angle the shorter the length of the impact area. Since there is no possibility to influence the ballistic factor of the fragments, the only possibility to reduce the impact area is to choose a steep entry angle. At 7 = - 5 ° the debris are distributed over a distance of about 250-300 km compared to 1500 km at 7 -- - 1°. The velocity impulse necessary for de-orbiting depends mainly on the desired entry angle: the steeper the entry angle the higher the V demand. For a return from a 460 km circular orbit the A V velocities have been computed for three initial entry angles. The

959

1100

Assumptions: • Return from 460 km circular orbit • Entry altitude 120 km • BaLListic factor of grnents: /~1 = l O O k g / m Z

1000 900 800 ¢n

700

E

600

~2 =

500

~3 = I OOOkg/m 2 ~4 = 2000 kg/m2

•

400

400kg/m

2

5OO

200100 I

AV= 2 5 0 m / s ~ . . . . . . . _ _ ~ I

0

I

I

~

100

I

I

I

I

500

I

I

I

I

I

1ooo

II 1500

I

Design point Length

of impact area [km]

Fig. 2. AV vs length of impact area.

respective propellant masses have been calculated for a vehicle mass of 9200 kg. As the figures indicate, it seems to be of no considerable advantage to choose an entry angle steeper than - 5 ° because the AV demand (and hence the propellant consumption) increases exponentially while the reduction of the impact area is only marginal (Fig. 2). Figure 3 shows impact areas for a shallow reentry (7 = - 1o). Despite the assumption that no side forces act on the descending fragments, a lateal displacement of 300 km has to be taken into account. This corresponds to the optimum cross range capability of a low lift/drag vehicle (capsule type) and therefore it should represent a safety margin. The footprints for the steeper entries (7 = - 5 ° and - 1 0 °) are located within the shaded areas in the figure. For return from an orbit inclined 28.5 °, as foreseen for the ISS, the impact area obviously will be located between + 28.5 ° latitude.

Dvor

50

j

LA'~ '(enned

.

"O -i

"6 .J

J

°r.o

---b--L

-2 -60

-180-150

if20-90-60

-30

0

Longitude

Fig. 3. Ground track and debris area•

Table 1. Dependencyof AV and impact area of entry angle Length of Sp~ific Propellant Entry angle impactarea RequiredAV impulse consumption (deg) (km) (m/s) (s) (kg) - 1 1500 110 315 327 -5 300 390 315 1108 - 10 150 1080 315 2750

50

960

N. DEUTSCHERet al.

It should be noted that there are several other impact areas beside those suggested in the plot. Furthermore, those areas probably can be approached either from the north or from the south, depending on the orbital ground track. Some constraints on the choice of a suitable impact area may be imposed by availability of ground stations required for tracking and initiation of the re-entry manoeuvre. 6. GENERAL REQUIREMENTS

• The ATV has to be AR5-compatible, as well as ISS, M T F F and OMV compatible. • The ATV shall be able to transport the logistic modules compatible with STS and U.S.-expendable launchers• • The ATV shall be designed to steer the AR5 lower composite during ascent. • The ATV shall satisfy the worst case AR5 launch load factors. • The ATV has to accommodate cargo for disposal during controlled destructive re-entry. • During docked phase the ATV shall be able to •accept power from other sources. • A sufficient propellant quantity for all orbit manoeuvres, including a 10% error margin, must be guaranteed.

height is driven by the equipment implementation and pressurized module installation. The VEB has to support additional and new electronic boxes, plus additional hydrazine tanks. The VEB structure is compatible with this additional mass. Only local re-inforcements may be necessary. The adaptor supports new heavy equipment, internally mounted as well as externally mounted new sensors. Lithium cells may be externally mounted if there are some late access problems. Due to ground integration, the hydrazine system is placed completely on the VEB and the cold gas system is integrated on the adaptor. A pyrotechnic separation system will provide the separation of the VEB/adaptor from the payload. 7.3. L 5 modification

The L5A four-tank sandwich architecture with SPAR-WEB structures will be reused (Fig. 6). The

Logistic vehicle RVD Docking mechanism

PayLoad module 7. T H E ATV ARCHITECTURE

7.1. General architecture

• An upgraded AR5/L5 stage, which will perform the required boosts for orbit transfers and homing manoeuvres. c A n upgraded AR5/VEB, which ensures the control-command of the vehicle. • The payload adaptor, ensuring interfaces to the payload and supporting most of the ATV additional equipment• • The RVD-kit, which will be mounted on the P/L-module. ATV will provide the same functions as the standard L5 and VEB during launch. Upgrading of these two elements has been carried out so as to allow ATV to fulfil the various mission requirements. However, in order to minimize the impacts of the ATV mission on the standard AR5 elements, their overall architecture and equipment will be kept unchanged as far as possible. Figure 4 shows the major parts of the ATV: completing the ATV with a P/L-module results in a logistic vehicle.

ATV

ATVMajor parts -~'~ .

R V D Kit detachable

P / L - adaptor support structure

VEB VehicLe equipment. bay

7.2. VEB and adaptor

A cylindrical 4 mm din adaptor is mounted on the upper side of the AR5-L5 stage (Fig. 5). A specific interface ring is mounted on the top for the adaptation to larger P/L-modules and for the separation of the ATV from the payload-module. The adaptor

LS-Stage A R 5 - Upper stage

Fig. 4. Main ATV constituents.

\

\

\

._A I-I

,-~---r=-

Y A

:ig. 5. VEB/adaptor configuration (solid parts, ATV modifications).

~

.~,.[..n~....X

f,m

:l.

I

°

-1~16.4

i

r~

rig. 6. Selected architecture.

F[L OR 'L^!

:ILL AND DRAIN

J

13

'3

_t

Ariane transfer vehicle propellant tanks will be suspended equatorially. An inherent growth potential exists due to tank enlargement without increasing the L5 stage length. The structure frequencies are better than demanded by the requirements. An ATV special enhancement concerns the thermal protection by MLI. For providing a passive thermal conditioning with the aim to avoid electrical power consumption for an active heater control 20 m2/s MLI with a weight of 20 kg is needed.

963

7.4. A T V main engine enhancement • The principle: Because of safety reasons, the four-tank version is used, the tanks being subdivided into two pairs, one oxidizer and one fuel tank each. One pair is used for up-transfer, the other one is used for deboost (Fig. 7). • The safety approach: During the up-transfer the whole piping of

FN<

r,~vH

;v, it

LYH~.4 --I

LYM~

~VM

~wV

i

TP

LVN[ ~ ! !

I FiLL-AND bRAIN

I I COUPLINGS I

/vIMH

II

,,,.'1h¢/..¢-

I

!m

VEB~f

IBM

Fig. 7. ATV propulsion system (shaded areas, L5 enhancements).

I i FILL-AND I DRAIN I COUPLINGS I

N. DEUTSCh'ERet al.

964

PROXIMITY I ATrACHEDIIDEORBITATION| II'H°MINGIIOPERATIONS,I PHASE |

PHASES

PHASING &l TRANSFER

MODES

'~ , , ' ~ A F E ~ " ~ ~ / . / I / / /

Fig. 8. Phases and modes.

tank-pair 2 is empty and all of its valves are closed. After the up-transfer and before ATV docking to the orbital target all of the residuals and the piping of pair 1 are cleared and all of the valves are closed. This concept leads to the following benefits: the freezing of the piping and of any valves can be avoided the necessity to avoid an explosion of residuals in the piping can be provided heating problems are avoided. • The upgrading of the L5A consists of the following parts: - - one latchvalve in GN2 circuit a total of six additional valves included drive valves for redundancy are provided in the second oxidizer piping one additional ACS is provided. -

-

-

-

-

-

-

-

-

-

8. DYNAMICAL CONFIGURATION

Principally, the definition of the modes depends on both the operations and the design (Fig. 8). The identification of modes is helpful for assessing which functions and equipment are necessary during the mission, which constraints influence the configuration or how many identical equipment are active with respect to safety rules. The definition of modes is necessary for sizing several subsystems, the power budget and other items.

The principal phases are the launch, the phasing and transfer from the injection point fixed by AR5 second stage burn up to a 460 km circular orbit, homing and the proximity operations next to ISS/MTFF 2. After having been attached to the Space Station, the de-orbitation manoeuvre for the purpose of re-entry, being started with safe retreat from the Space Station, represents the last phase. During phasing and transfer one can differ between the modes of low phasing with minimum power consumption and high phasing with respect to the above mentioned intermediate orbit, these modes being relatively short boost phases necessary for orbit transfer. A safe emergency mode can be reached from each of the proximity operations or station keeping modes. Concerning the safety during proximity operations the following considerations have to be taken into account: • The ATV will carry out the proximity operations on a collision avoidance orbit (Fig. 9). Executing a V-bar approach free arcs between a 1 km to a 100 m ATV/ISS distance allow a failure of firing for each of the thrusters. • It follows a forced trajectory within a 100 m distance with a velocity law adapted to have ATV permanently on a collision avoidance orbit, except for the last few meters.

~oo._z~

~

Proximity operotions(ATV,choser,lSS)

1k m ~

50m

!

k 100 m

30 rn

Fig. 9, Proximity operations.

z

t

•] 300 m

Fig. 10. Emergency operations.

Ariane transfer vehicle • Within 30 m distance from A T V to ISS, only the cold gas thrusters may fire. • With current ISS design, the centre of gravity of the A T V is below that of the ISS. Thus, without propulsion, the A T V is naturally moving away. • In case of emergency (Fig. 10), i.e. after two major failures, a safe retreat capability is given by hydrazine or cold gas thrusters. During its autonomous flight, the A T V is threeaxis stabilized and Earth pointed; - - from A R 5 separation to proximity operations, the longitudinal axis is aligned with the velocity vector; -for proximity operations until berthing, the longitudinal axis is pointed towards Earth. When attached to ISS, ATV is oriented as for proximity operations. 9. AV AND PROPELLANT BUDGET ISS-MISSION ( T A B L E S 2--4) With the aim of adding up the A T V propellant needs towards ISS a A V budget is necessary. In Table 2 the needed A V for each mission phase is given. The logistic vehicle (LV) is delivered by AR5 into a 135 x 300km, i = 2 8 . 5 ° elliptical transfer orbit. After phasing in this intial transfer orbit an orbit change will get the LV to a circular 460 km orbit by two burns of the ATV main engine, one at the perigee and the other one at the apogee of a 300 x 460 km

965

transfer orbit. This orbit change will demand about 95% of all of the A V, i.e. all of the propellant needed for ascent. A H o h m a n n transfer to the final orbit will need some 4 % of the total AV required for ascent. Concerning the proximity operations, A V can be nearly neglected. Concerning the deboost a 250 m/s AV is needed. H o w to get to this amount of AV is explained previously in Section 5. Though the A V budget for ascent is, with 150 m/s, about 100 m/s less than the AV needed for deboost, the total fuel needs for ascent are about 100kg greater than those for re-entry because of a relatively high LV-mass during ascent. Bipropellants will be used for orbit transfer manoeuvres with a high demand of V and hydrazine for manoeuvres with low need of A V. 10. ATV-ISS LOGISTICS FLIGHT MASS BUDGET As can be seen in the Fig. 11, the ATV dry mass composes of its three, above mentioned basic elements: the upgraded VEB, the upgraded L5 and the payload adapter. Each of these major parts can be subdivided into its main subsystem including structure, electrical system and other equipment. Thus, the ATV dry mass is about 2700 kg. Considering the logistic flight toward ISS, propellants of 1760 kg must be taken on-board. Considering a P/L-module of 5.4 Mg and a payload of about 7.3 Mg the total mass of the LV gets to some more than 17 Mg. This is within the A R 5 P/L-capacity.

Table 2. AV and propellant budget ISS-mission Needed AV Fuel mass (m/s) (kg) Delivery of ATV by Ariane in 135 x 300 kin: i =28.5 ° Transfer to 460 x 460 km Transfer to 470 x 470 km Drift orbit to 1 km in front ISS Deboost Sum bi-prop. Sum hydraz.

96 45 2.8 2.8 0.4 0.4 250 391 6.4

530 246 22 21 3 3 730 1506 49

Table 3. ATV propellant budget Bi-prop. Hydrazin Task (kg) (kg) Orbit transfers 776 49 Deboost 730 Launch 13 Pre-acceleration 27 Proximity operations 70 Attitude control <1 Total 1506 160

Initial ATV mass Main engine SCA hydrazine system Cold gas systems

Bi-prop. Bi-prop. Hydraz. Hydraz. Hydraz. Hydraz. Bi-prop.

Cold gas (kg)

56 56

Table 4. ATV p r o p u l s i o n 17,200 kg l,p--315 s 27.5 kN bi-prop. I,p--220 s 350 N hydrazine I,p--66 s 10 N GN2

Burn time (s) 59.5 27.6 132.4 132.4 19 19 90

966

N. DEUTSCHERet al.

190 kg

ADAPTOR VEB

//"

1200 kg

VEB - UPGRADE

400 kg

L5

832 kg

L5 - UPGRADE

57 kg 2 6 7 9 kg

A T V DRY MASS

VEB- MASS BUDGET BASIC YES AVIONICS

L5 MASS BUDGET

30 kg

TANK STRUCTURE PROPULSION SYSTEM STAGE STRUCTURE STRUCTURE SUPPORT ELICTRICAL SYSTEM SELFDESTRUCTION SYSTEM PROTECTION SHIELD THERMALPROTECTION GIMDAL STRUCTURE PIPING etc. ENGINE SAFETY UPGRADE

90 Kg

STAGE

1200 I
S CA ELECTRICAL SYSTEM VARIOUS

160 kO

ADAPTOR -

MASS BUDGET

82 kg STRUCTURE STRUCTURE

VED -

DRY ttt.SS

Ieoo kg

30 kg SUPPORT

COLOGAS SYSTEM INTERFACE RING

ADAPTOR

DRY MASS

238 kg 202 k0 109 k S 21 kg 65 kg Ilkg 5 kg 25 I~g 411 kg 54 kg 37 Iq; 889 kg

40 kg

DRY MASS

190 kg

Fig. 11. ATV-ISS logistics flight mass budget. II. COMMUNICATIONSUBSYSTEM(FIG. 12) A communication subsystem will be provided guaranteeing coherence and commonality with other programs: Hermes or Columbus as well as Ariane 5. ATV required additional or new equipment S-band system Ku-band system TM/TC

The ATV is in direct communication with the ground during phasing and transfer. It communicates with ISS/MTFF step 2 or with ground via ISS/MTFF step 2 from homing phase. Communication via DRS is an option.

Reused from: 12. AVIONICSARCHITECTURE AR5 Hermes or Columbus Hermes

The avionics architecture, as illustrated in Fig. 13, is based on the reuse of Ariane 5 architecture.

1553 buses Sbond F1 ~.~ - -

Ku- bond l_ Receiver r

F3,._)

F4~_~

F2~ I Ku-bond I_

Re=ever

l-

Fig. 12. Communication subsystem,

R

Existing on A R 5

Ariane transfer vehicle

967 ISS/IF

"555 bus

Bus1

L5 AR5

/

I

I~

_"

BusZ~ "~

F ---

ISS/IF

55B bus

I L_

I __

I

~

Minimal

chain f o r withdraw

~

ExistingAR5

__J

•

Existing ARS,to be upgraded

Fig. 13. VEB block diagram, ATV serving as chaser.

If the ATV serves as target, two buses and two computers will be provided with access to both buses. In the case of the ATV serving as a chaser, three computers are foreseen. A third chain, corresponding to the safe withdrawal mode, is provided for safety reasons and gives the capability to escape from the vicinity of ISS/MTFF step 2 after two failures. Thus included are a TC unit and sequential electronics to control the hydrazine and the cold gas system. ATV navigation and attitude control is based on the use of the initial reference system (IRS) already mounted on the VEB. The IRS is updated before each main manoeuvre, or at least every 6 h, and is provided with star sensors.

13. ATV DEVELOPMENT PLAN The development plan shown in Fig. 14 has been set up considering the constraints coming from all of the systems and subsystems being involved in the ATV philosophy: GPS is used for orbit escalation. For proximity operations IRS, GPS and rendezvous sensors are used. For actuators, the hydrazine thrusters and the cold gas system are controlled by sequential electronics, both systems including four sets of four thrusters. The electrical energy is provided by lithium cells. For avionics, the power subsystem is composed of two buses, each of them powered by two lithium cells, and an emergency bus, powered by two AR5 lithium cells. A fifth lithium cell, which can be connected to each of the main buses, will be added for safety reasons. The total available electrical energy is 40 kWh. It is sized for 48 h autonomous mission plus margin. When being attached the ATV is able to accept power from I S S / M T F F step 2.

14. C O N C L U S I O N S

The proposed ATV concept fully complies with the philosophy of maximum use of existing AR5 hardware, to minimize the overall development and recurring costs. The ATV meets all the requirements identified to transport logistic resupplies to the ISS and M T F F . The safety requirements and the failure precautions in proximity operations follow, in principle, the standards of the Columbus/MTFF and Hermes scenarios. The ATV offers a wide flexibility to transport resupply logistics to space-based elements in LEO and to dispose the waste. It is able to tug as well pressurized as unpressurized P/L modules in several sizes (Columbus, Japanese, Titan). Due to commonality of the ATV hardware with basic AR5 hardware the ATV provides a great availability and a high degree of flexibility in terms of mission schedule. Stabilized Earth pointing mode with longitudinal axis along velocity vector allows for a good thermal control and minimizes the drag during phasing. ATV may be a chaser or a target. Concerning the equipment level most of the ATV hardware would be reused from AR5 or programs such as Hermes or Columbus. The development plan would be in line with AR5 and other programs planned. ATV would be a part of the European IOI. It would complete Hermes for the transport of logistic modules or large elements and allow the discard of nonrecoverable items.

Acknowledgement--The work presented in this paper

was

performed under ESA/ESTEC Contract No. 7357/87/NL/ MA(SC) in 1988.

1 2 3 4 5 6 7 8 9 10 11 12 13

1 2 :3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

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