On-orbit servicing

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Maintenance and repair work on the Hubble space telescope by astronauts Smith and Grunsfeld
Orbital Express: ASTRO and NEXTSat

On-Orbit Servicing (abbreviation: OOS) includes assembly, maintenance and repair work on an artificial object in orbit ( satellite , space station , spacecraft ) with the aim of extending the useful life of the target object and / or expanding its capabilities ( upgrade ). OOS can be divided into manned and unmanned missions.

background

Manned OOS missions

Manned OOS missions can be seen as part of manned spaceflight. Should a system component fail, the crew tries to repair or replace it, whether on a spaceship or a space station. In the following some successful OOS missions:

Unmanned OOS missions

While manned OOS missions inevitably belong to the standard in manned space travel, most of the unmanned missions are still on a theoretical-experimental level. The only system that is already ready for use is the Mission Extension Vehicle from Northrop Grumman .

In the following some projects and studies on OOS:

Projects carried out unmanned

Space Robot Technology Experiment (ROTEX, 1993):

The ROTEX (sensor-based robot arm) started in 1993 with the Spacelab - D2 mission of Columbia. The experiment successfully demonstrated that the milestones for robotic applications in space such as sensor-based and shared autonomy and real-time teleoperation are possible from a ground station.

Ranger Telerobotic Flight Experiment (RFX / TFX, 1993-2005):

The Space Systems Laboratory at the University of Maryland is dedicated to ensuring that robotic systems productively support humans on space walks. The Ranger Telerobotic Flight Experiment (RTFX or TFX) began in 1993 and was supposed to be a scientific mission with the aim of obtaining a database in the relationship between a repair satellite and a ground station simulation. A satellite and a similar underwater version (Neutral Buoyancy Vehicle, NBV) were planned for this experiment. The TFX program became the Ranger Telerobotic Shuttle Experiment (RTSX or TSX) in 1996. However, in 2001 the financial support from NASA was stopped.

Engineering Test Satellite VII (ETS-VII) with GETEX (1998)

Robotics Component Verification on ISS (ROKVISS, 2005–2010):

ROKVISS was an experiment to test robotic components under space conditions. At the end of January 2005, the two-jointed robotic arm with its platform was installed on the Russian service module of the ISS. The communication link was a direct radio link, which means that its connection to the ground station can only be maintained for a maximum of eight minutes per orbit.

Further:

Concepts and Studies

Experimental Servicing Satellite (ESS, 1993):

The ESS study and the laboratory demonstrator provided for it were started after the successful ROTEX mission (1993). The aim of this study was to determine the dynamic behavior during rendezvous and docking maneuvers. For this purpose, a docking mechanism has been developed which can latch into the apogee engine of the target satellite (if available).

Spacecraft Modular Architecture Design For On-Orbit Servicing (SMARD, 1996):

The SMARD study evaluated the cost-benefit ratio of OOS missions. One concept provided for the stationing of 10 or fewer repair satellites in the LEO on different orbit planes. These can then be used for OOS, but the satellites to be repaired must be OOS-capable.

Operational Servicing Satellite (ESS - OSS, 1999):

The ESS-OOS study was commissioned due to the ROSAT development, in which no engines were intended for re-entry initiation. This study aimed to investigate possible capture and re-entry strategies .

Spacecraft Life Extension System (SLES, ~ 2002):

The SLES, which was developed in cooperation between DLR and Orbital Recovery Corp. was to be developed, provided for a repair satellite that is to dock with a compromised telecommunications satellite in the GEO, using the system developed in the ESS study to take over its propulsion, attitude control and navigation system. Alternatively, a stranded satellite should be able to be maneuvered into the correct orbit.

Robotic Geostationary orbit Restorer (ROGER, 2002):

ROGER was initiated by ESA in 2002 as a feasibility study to capture an unintended geostationary satellite and perform an orbit maneuver. DLR was involved in the analysis of the two strategies. One concept envisaged a rope and the other a gripper when carrying out the capture action.

Technology Satellite for Demonstration and Verification of Space Systems (TECSAS, 2001-2006):

ECSAS was a German-Russian project for the qualification of robotic components, which was initiated in 2001. The implementation of the mission envisaged a rendezvous, an approach, an orbital maneuver for inspection, a formation flight and other maneuvers for trapping and manipulating. The project was stopped in 2006. The findings were transferred to the German Orbital Servicing Mission (DEOS, 2007) project.

German Orbital Servicing Mission (DEOS, 2013-2018):

The DLR's DEOS project was intended to collect data relating to a system solution for recovering damaged satellites from orbits. The aim of the mission, which was due to start at the end of 2017, was to test the safe approach and capture of uncontrolled satellites. The mission would have consisted of two satellites, one simulating the wrecked satellite and the other being used for technology testing. The project was abandoned in 2018.

Types of OOS missions

The following types of OOS can be identified in the literature:

  • Refueling : Refilling the consumables at the target satellite with z. B. fuel, coolant, ...
  • Orbit maneuver : Correction of the orbit orbit after incorrect orbit injection by the transfer stage or premature target satellite failure before it could be transferred to the cemetery orbit .
  • Repair : A simple case of damage, such as a failure to extend an antenna, or a complex case of damage, which means the failure of a component, could be repaired. If the target satellite is not intended for repair, complex damage cases can sometimes not be repaired.
  • Upgrade : Exchange of system components with components of the latest technology, which enable an increase in the usefulness of the target satellite.
  • Building and assembling large structures : The principle of building large structures is called “Born-in-space architecture” in NASA. Here, large structures are built up modularly and the subsystems are combined in orbit to form an object.
  • Space debris disposal: The disposal of space debris is a kind of "orbit maneuver", whereby the target object (defective satellite, burned-out upper stage, ...) is transferred to a re-entry orbit. The background to this is the idea, known as Kessler's syndrome, that if space debris continues to increase, space travel may no longer be possible.

Further considerations in this direction lead to the establishment of depots for consumer goods. The Hermes concept takes up this idea with the payload station. This enables the repair / service satellite to fly to several target satellites in order to carry out a service.

In his dissertation, Sullivan was able to identify five types of service or error and their error frequency. These provide information about which listed OOS type occurs most frequently and thus has the greatest potential:

  1. 57.4%: Complex maintenance, repair and repair work
  2. 17.7%: orbit maneuvers
  3. 12.1%: inspection
  4. 7.8%: refueling
  5. 5.0%: Simple maintenance, repair and repair work

The list shows that the failure of components (complex repair work / damage) is one of the most frequent causes of failure. Since this represents the greatest challenge to the technology of the repair satellite and the service time is considerably extended, if the replacement of a component is even possible, the design philosophy of the Orbital Replacement Unit was developed. This is intended to significantly reduce the cost of the service, so that complex repair work is transformed into simple one.

Orbital Replacement Unit

The Orbital Replacement Unit concept (ORU) is a design philosophy for artificial space objects such as satellites, spaceships and space stations. The satellite is divided into modules in such a way that they can be exchanged during a service mission without any major problems. The main focus is on size, accessibility and easy-to-connect interfaces to the rest of the satellite. Examples of the application of this concept are e.g. B. the Solar Maximum Mission , the Hubble Space Telescope and the International Space Station .

A typical ORU on the Hubble Space Telescope is referred to as a separate box on the satellite that can be mounted and dismounted using locks and connectors.

Framework

Satellite distribution in the GEO
Satellite distribution in the GEO (detailed excerpt)
Satellite distribution in the LEO
Satellite distribution in the LEO (detailed excerpt)

In the following, the object satellite is used as an example for the sake of simplicity, but the framework conditions refer to objects (satellite, space station, spaceship, space debris, ...). The general conditions are the same, but slight variations may occur. Eight categories / framework conditions could be identified in the NASA study. The following four points largely coincide with the eight categories of the NASA study:

Location of the target satellite - has an impact on: economic potential, the telecommunication connection, the service satellite, the type of mission

The location of the target satellites, whether close to earth ( LEO , GEO , ...) or remote ( Lagrange points sun-earth, Mars , ...), has an influence on the type of satellites that are present at the target location (military, commercial or scientific). The various areas will (can) spend different amounts of money on service issues. In addition to the type of satellite, the accessibility of several target satellites is also important. For example, changes in orbit inclination in the LEO (even less than 1 °) require extremely high fuel consumption due to the high orbit speed, which means that a service mission usually only includes reaching a target satellite. In the GEO, on the other hand, most satellites are close to each other from the orbital inclination point of view and due to the lower orbit speed changes in orbital inclination are not as fuel-intensive (see diagrams for satellite distribution). Another challenge is caused by the changing environmental conditions, which in turn determine the design of the service satellite (service life, redundancies, ...). The next problem of the location is related to the distance to the control center. The telecommunication connection influences the type of robotic service mission. This can be compensated for by combining manned and unmanned missions (the robots for EVA use ).

Status of the target satellite - affects: the type of mission, the service satellite

Status can be used to describe the state during the implementation of an OOS mission and its design. The state can be controllable or not controllable, which makes it difficult to approach and capture the target object. A fringe area in this context are military satellites, which could possibly have a defense system against approaching satellites. Furthermore, the design of the target satellite can be designed for a service mission (through service interfaces, ORU, ...). If this is not the case, the service process is made considerably more difficult, so that an OOS mission z. B. can only be carried out manned.

Telecommunication connection - affects: the type of mission, the service satellite

The possible communication time (LEO satellite with a ground station approx. 10 min per orbit) and the time required to transmit information (between earth and GEO satellites: 2 × 35,000 km / 300,000 km / s ~ 1/20 s) have a considerable influence on robotic service missions. Robotic missions can be telepresent, partially or fully autonomous: degree of automation. If there is only a short connection time (e.g. 5.10 minutes per overflight), telepresent missions may not be able to be carried out because the time required to carry out an action is too short. Furthermore, telepresent missions cannot be carried out if the transmission time is too long (delay between sending the command and carrying out the action). The lower the automation, the higher the volume of data that has to be exchanged between the control center and the service satellite. The data volume determines the frequency band required.

Mission type - has an impact on: the service satellite

A service mission can be manned or unmanned. However, a manned mission can be supported by robotic systems. The type of mission depends mainly on the service task on the target satellite, i. H. how complex is the task that has to be performed? The lower the task complexity (e.g. refueling with an interface provided on the satellite), the sooner a fully autonomous unmanned mission can be carried out.

Advantages and disadvantages

The disadvantages of an OOS mission are usually not explicitly stated in the literature. However, these can be extrapolated from the consideration of how a target satellite should be structured. On the one hand, there is an increase in mass, since components must be easily accessible for exchange and the interfaces must be clearly defined and available. This has an effect on the development costs (additional framework conditions). The associated increase in mass has an impact on transport costs and fuel mass, which in turn determines the service life of the satellite. Furthermore, there is still no service infrastructure, so satellite manufacturers would not currently design their satellites for this.

Advantages of OOS missions, once the infrastructure exists, would be:

  • Reduction of the risk of mission disruptions / failures : Should disruptions occur during a mission, such as the failure of components or the failure to reach the target orbit, these errors can be rectified and the mission can be continued without further impairments.
  • Reduction of the mission costs : This is made possible by the fact that the satellite manufacturers are allowed to build in lower redundancies and the components could be designed for a shorter service life. This also enables a separation into high-quality and low-quality components (e.g. hardware vs. fuel), which in turn influences the choice of the carrier system with regard to reliability / costs.
  • Increase in the mission benefit: Scientific missions in particular can benefit from upgrades, as technological development often progresses faster so that the hardware is no longer up to date when the mission is carried out. This becomes particularly clear with missions lasting> 5–10 years, where several years of development and production time have already passed.
  • Increase in mission flexibility: This flexibility is achieved by exchanging hardware. These upgrades could not only improve existing instruments, but also incorporate new components that pursue a new mission objective.
  • Enabling new types of missions : In this area, the “Born in-space architecture” is of particular interest. This enables novel concepts, which in turn have an influence on the mission design. One of these structures is the ISS.

literature

Web links

Individual evidence

  1. ↑ a b c d On-Orbit Satellite Servicing Study - Project Report. (PDF; 7.2 MB) NASA , October 2010, accessed on July 17, 2011 (English).
  2. ↑ a b c D. Reintsema, K. Landmarke, G. Hirzinger: DLR's Advanced Telerobotic Concepts and Experiments for On-Orbit Servicing. DLR, August 2007, accessed on July 7, 2011 (English).
  3. ^ Dexterous Robotics at the Space Systems Laboratory. University of Maryland, archived from the original on June 23, 2012 ; accessed on July 9, 2011 (English).
  4. ↑ a b c d DLR, Institute of Robotics and Mechatronics, Status Report 1997-2004 (English)
  5. ↑ a b Reynerson Dr. Charles M .: "Spacecraft Modular Architecture Design", Study Final Report, October 18, 1996, Naval Research Laboratory
  6. ↑ a b Homepage: Ongoing Space Robotics Missions - TECSAS / DEOS. DLR , accessed on July 17, 2011 (English).
  7. ↑ DEOS - German Orbital Servicing Mission. DLR Services, archived from the original on October 5, 2013 ; Retrieved November 16, 2013 .
  8. ↑ DEOS on Gunter's Space Page, accessed on September 6, 2019.
  9. ^ A b Sullivan Brook Rowland: Technical and Economic Feasibility of Telerobotic On-Orbit Satellite Servicing, University of Maryland, 2005
  10. ↑ Hubble Space Telescope - Media Guide. (PDF; 3.3 MB) NASA, accessed on July 29, 2011 (English).