Www.southampton.ac.uk/engineering | email: [email protected] Astronautics Research Group, Faculty...
If you can't read please download the document
Www.southampton.ac.uk/engineering | email: [email protected] Astronautics Research Group, Faculty of Engineering and the Environment University of Southampton,
www.southampton.ac.uk/engineering | email: [email protected]
Astronautics Research Group, Faculty of Engineering and the
Environment University of Southampton, Southampton SO17 1BJ, United
Kingdom IAC-14-A6.P.58 Hugh G. Lewis & Aleksander Lidtke Active
Debris Removal: Consequences of Mission Failure Motivation There is
widespread belief that Active Debris Removal (ADR) is needed to
reduce the hazard posed by an increasing space debris population in
low Earth orbit (LEO). Evolutionary models have demonstrated that
the sustained removal of a few large debris objects can have a
beneficial effect on the LEO debris environment. Following these
studies, there has been a drive towards the development of
technologies and concepts for ADR, with several on-orbit
demonstration missions now proposed. However, the ubiquitous
assumption made in modelling studies and the subsequent concept
development has been that ADR always results in a successful
mission outcome, i.e. the ultimate removal from orbit of the
targeted debris and the chaser vehicle used. This is unrealistic,
given that traditional space missions can, and do, fail on-orbit.
Of real concern, therefore, is the potential for ADR to add to the
space debris hazard. Three mechanisms exist through which the
benefits of ADR may be lost: key debris targets may not be
retrieved, new debris may be added in the form of failed chaser
vehicles, or collisions involving the former objects may occur. The
last mechanism is of particular concern because debris targets and
failed chaser vehicles will be in highly populated regions of LEO.
This research aimed to address the concern, through simulations of
these mechanisms using the University of Southamptons debris
evolutionary model DAMAGE. In so doing, recommendations for ADR
mission reliability and programmatic approach were identified. LEO
population growth 2013-2113 Fraction of all Monte Carlo runs
showing population growth Fraction of all collisions involving a
failed ADR chaser vehicle Fraction of all removal missions
targeting a failed ADR chaser vehicle Method Two ADR mission
approaches were studied: a single-removal chaser vehicle that
removed only one debris target before de-orbiting itself, and a
multiple-removal chaser vehicle that removed five debris targets
before de-orbiting. In the latter case, it was assumed that the
chaser vehicle attached a de-orbit device (e.g. drag sail, tether
or solid rocket motor) to each debris target before performing an
orbit transfer to the next debris target and repeating the
procedure. Consequently, a failure of the multiple-removal chaser
vehicle would only have consequences for debris targets yet to be
visited. Launch vehicles associated with the ADR chaser vehicles
were assumed to de-orbit immediately following the payload
separation. Five different chaser vehicle failure rates were
simulated: 0%, 5%, 15%, 30% and 45% per year, with vehicles
selected randomly, and three removal rates: 5, 10 and 15 debris
objects per year (with the addition of a baseline case with no
removals used for comparison). In addition, it was assumed that a
mission failure resulted in the complete loss of control of the ADR
chaser vehicle, which remained on orbit. ADR chaser vehicles
successfully completing their mission were removed from orbit
immediately. Failures were assumed to occur in one of three
positions, selected randomly, relative to the target debris: (1) in
a drift phase 100 km below, (2) in an inspection phase 50 m below,
or (3) in a contact phase. The probabilities associated with each
position were 50%, 25% and 25%, respectively. Failed missions were
not repeated in the same year. Projections of the LEO debris
population 10 cm from 2013 through 2113 were performed using
DAMAGE, with 50 Monte Carlo (MC) runs used for each scenario.
Conclusions A multiple-removal chaser vehicle provided substantial
benefits in terms of robustness to failure, compared with the
single-removal chaser vehicle approach. However, such missions are
inherently more complex and involve potentially greater risk of
failure, given the need for multiple proximity operations. Further
work is required to understand the effect of this trade-off. The
single-removal chaser vehicle approach resulted in a significant
effort (up to 35% of removal missions) focused on removing failed
ADR chaser vehicles, and up to one-in-four collisions involved an
ADR chaser vehicle (27% of all collisions). The results also showed
that debris removal rates of more than five objects per year were
needed to prevent, or limit, the growth of the LEO population over
100 years. At the same time, a higher number of removals required a
corresponding decrease in the individual mission failure rate (i.e.
an increase in reliability) to achieve the same outcome, for both
types of mission. The effect of higher failure rates was an
increasing probability that the LEO debris population would grow in
number. Future efforts in ADR must move beyond the assumption of
immunity to failure: consideration needs to be given to ADR
technologies and concepts that are robust to failure and result in
a benign impact on the environment in case of failure. Without such
a move, there is a possibility that a remediation method, widely
perceived as the only solution to the growing space debris hazard,
could exacerbate the problem. Effective number of objects (LEO, 10
cm) Year Population density as a function of time for failure
scenarios involving single-removal ADR missions launched at a rate
of 10 per year No failures; No removals No failures; Target: 10
removals per year 5% failures; Target: 10 removals per year 15%
failures; Target: 10 removals per year 45% failures; Target: 10
removals per year Results Charts showing the population density,
LEO population growth (compared with the 2013 population), number
of MC runs in which population growth was observed, fraction of
collisions involving failed ADR chaser vehicles and fraction of
removal missions that targeted failed ADR chaser vehicles, are
reported here. Single-removal Multiple-removal Single-removal
Multiple-removal Single-removal Multiple-removal Single-removal
Multiple-removal Acknowledgements Thanks to Holger Krag, Head of
the ESA Space Debris Office, for permission to use the MASTER
reference population within DAMAGE, and colleagues from IADC WG2
for comments on an earlier report on these results.