Trampoline Deorbiting System
Version 1.1
Copyright 2017 by Paul Niquette. All rights reserved.
Earth Orbits
A visualization of orbital debris.
NASA Orbital Debris Program Office

orbital debris As of this writing (mid-2017) some 18,000 man-made objects are orbiting the earth, including more than 1,400 operational satellites (see Table 1).  Mankind depends on uncountable applications of space technology; many of the most vital applications can be categorized as follows:

 {1} Astronomical Observations are conducted by Hubble in orbit above the atmosphere.
 {2} Broadcasting Networks
are supported by hundreds of geostationary earth orbits.

 {3} Communication Services use constellations of satellites in polar orbits.
 {4} Debris Remediation requires specialized satellites deployed in various orbits.
 {5} Intelligence Gathering must operate at low orbital elevations for close-up imaging.
 {6} Mapping Services are operated by governments and businesses worldwide.
 {7} Meteorological Imaging satellites operate in asynchronous or geostationary orbits.
 {8} Navigation Services use upwards of a hundred satellites in three constellations.
 {9} Scientific Experiments are conducted in a wide range of satellites.
{10} Space Station, most prominently the ISS, is deployed in a low-earth orbit (LEO).

Solvers are invited to observe that item {4}
Debris Remediation has been emphasized, signifying the vital need for mankind to address an international problem above the atmosphere, which is as challenging as global climate change within the atmosphere.

Orbital debris cluttering up space around our planet...
Size Categories
Quantities in Orbits
larger than 10 cm
1 to 10 cm
smaller than 1 cm

170 million

Since the beginning of the present century, the growing amount of man-made space debris in the vicinity of our planet has become a hazard to active satellites and spacecraft -- a threat, which is now far greater than micrometeoroids. 

All objects in space travel in orbits.  A typical object in low-Earth-orbit (LEO) is traveling at 28,000 km/h (17,500 mph). 

Never mind head-on or oblique-angle collisions, consider the case of a satellite and a piece of space debris traveling at the same velocity in orbits that cross each other at merely one degree.  They would collide with a relative velocity of 490 km/h (305 mph).  About like a dragster sideswiping a parked minivan.
Mankind ought to be embarrassed to look back over six decades at the reckless way nations of the world have treated the orbits of the world...
  • sending up ginormous numbers of satellites without providing for their end-of-life passification -- let alone disposal,
  • allowing discarded rocket boosters to settle into orbits, many loaded with explosive liquids, toxic waste, and radioactive effluvia, and worst of all...
  • conducting anti-satellite weapons tests, which gleefully blast spacecraft debris of all sizes every which way in space, expanding into bands of junk orbits.

Inasmuch as collisions with debris produce more debris, the resulting avalanche of destructive events, called the Kessler Syndrome, may soon enough render Earth orbits impassable for centuries.  Already, an average of one satellite is destroyed per year. 

There is really only one remedy for orbital debris: atmospheric disposal.

Every object in orbit will eventually get dragged down into the atmosphere.  The value of the word "eventually" can be immense, depending on orbital elevation.  Note {4} in Table 1 reads, "
Satellites or space debris in orbits at or below ~250 km (155 mi) will burn up in the atmosphere within one year."
Orbital decay can take a mighty long time.  That's good news for all of the satellite applications listed above.  As for debris...not so much.  To reduce hazards for spacecraft transiting debris-filled orbits, mankind urgently needs to figure out how to hasten the orbital decay of debris -- hey, to deorbit debris.
According to the NASA Orbital Debris Program Office, addressing risks to the current fleet of operational spacecraft, calls for remediation measures that emphasize the removal of small sized debris.  However, the control of long-term sources of fragmentation debris from on-orbit explosions and collisions, calls for the deorbiting of massive objects such as intact rocket bodies and non-functional satellites.  Quoting from a recent report: "Studies have indicated that the removal of as few as five of the highest risk objects per year can stabilize the long-term low-Earth-orbit (LEO) debris environment."

orbital debrisThe solution page for the Trampoline Deorbiting System puzzle puts forward a cost-effective proposal for rapid removal of "highest risk objects" from low-Earth-orbits, applying proven space-age technology in straightforward designs, which seem not to be described anywhere on the Internet.  Yet.
We might define "high risk objects" as [a] satellites which have completed their missions but nevertheless remain in orbit or [b] rocket boosters which have been abandoned perforce into orbits.  For brevity, let's adopt the term derelict.
Removal of a derelict requires a system designed to perform five generalized tasks:
Task 1: Launch and insert spacecraft into parking orbit above derelict orbit.
As part of the launch sequence, the spacecraft will be programmed by the ground base control center for autonomous operation. Here and throughout the mission, a form of 'orbital hygiene' needs to be mandated.  The rocket stages and spacecraft fairings, for example, must not be discarded into Earth orbits.  In that regard, a reusable launch system would be ideal.  
Task 2: Transfer spacecraft into derelict orbit for rendezvous with derelict.
The parking orbit matches the derelict orbit in inclination and eccentricity but has a slightly longer period.  As the derelict approaches conjunction from below, the spacecraft performs an autonomous orbit transfer maneuver using retrograde burns of its main engine. 
Task 3: Maneuver spacecraft into position and prepare for capturing derelict.
Because of expected irregularities in the structure of the derelict and its random orientation, attitude thrusters on the spacecraft must be operated in a remote robotic mode to make fine adjustments for rendezvous guided from the ground based control center using real-time video information.  Equipment on the spacecraft must be deployed and armed as necessary.
Task 4: Capture derelict and prepare for deorbiting maneuvers.
Various capturing mechanisms have been proposed, including harpoons and lassos and grappling hooks.  The most popular mechanism seems to be a huge butterfly-net catapulted from the spacecraft, as shown in this video clip of a test in synthetic weightlessness.
Task 5: Transport spacecraft and derelict into atmospheric disposal orbit.
Connected by cable, the derelict can only be towed by the spacecraft to the lower orbit required for disposal.  This imposes a technical challenge: The hot flames from the main engine during retrograde burns must be prevented from prematurely cutting the cable.

Solvers are invited to invent a practical system to accomplish all five tasks.



Table 1 Parameters for Man-Made Earth Orbits

Elevation MSL Radial Distance Period Velocity Quantity Notes
Zone Description
km mi km mi hr km/h mph

HE0 High Earth Orbit 384,000 238,540 390,378 242,502

Disposal Orbits > 36,100 > 22,425 > 42,478 > 26,387

GEO & GSO 35,786 22,230 42,164 26,192 24 11,038 6,900 300+ {2}
High Earth Orbit 35,786 22,230 42,164 26,192

Disposal Orbits < 35,300 < 21,930 < 41,680 < 25,890

> 20,700 > 12,860 > 27,080 > 16,820

MEO Medium
Earth Orbit
35,786 22,230 42,164 26,192

Galileo 23,222 14,425 29,600 18,387 14 13,284 8,300 30
GPS 20,180 12,536 26,558 16,498 12 13,906 8,690 31
GLONASS 19,130 11,884 25,508 15,846 11 14,570 9,100 29
Earth Orbit
2,000 1,242 8,378 5,204

Disposal Orbits < 19,700 < 21,930 < 26,080 < 16,200

> 2,000 > 1,240 > 8,378 > 5,204

LEO Low Earth Orbit 2,000 1,242 8,378 5,204

Polar Orbiting 700 435 7,078 4,397

435 270 6,813 4,232

Iridium & SSO 620 385 6,998 4,347 1.67 26,329 16,455 72
Hubble 595 370 6,973 4,332 1.593 27,503 17,190 1
ISS 412 256 6,790 4,218 1.545 27,602 17,251 1
< 1year
250 155 6,628 4,117 ~1.445 ~28,820 ~18,000
Low Earth Orbit 0 0 6,378 3,962

HEO, Molniya - Apogee 38,552 24,100 44,930

3 {5}
MEO, - Perigee 1,626 1,020 8,004

& Tundra - Apogee 38,552 24,100 44,930

3 {5}
LEO - Perigee 1,626 1,020 8,004

{1} Lunar orbit considered here to be the limit of High Earth Orbit.
{2} GEO, geostationary orbits, are all in the equatorial plane; GSO, geosynchronous orbits,
        are in non-equatorial planes.
{3} Polar orbits in this range have high inclinations with respect to the near-equatorial orbits.
{4} Satellites or space debris in orbits at or below ~250 km (155 mi) will burn up in the
        atmosphere within one year.
{5} Constellations of synchronous communications satellites in eccentric orbits for serving
        high and low latitudes.

Atmosperic Disposal

As shown in Table 1 there are three zones of Disposal Orbits.  These are put forward by the U.S. Government Orbital Debris Mitigation Standard Practices, which were endorsed by the United Nations in 2008.  A critical review of these voluntary practices is outside the scope of the Trampoline Deorbiting System puzzle. 
Solvers will surely observe that, since all forms of debris are subject to orbital decay, the act of moving derelicts into Disposal Orbits merely defers their inevitable endangerment of working satellites in orbits at lower elevations.