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NEED FOR DEBRIS REMEDIATION & REMOVAL CONCEPTS

Most debris is between 800km and 850km
Debris appears to be concentrated at higher inclinations

Large amount in Sun Sync, Large amount in 65º & 81º inclinations

Most mitigation strategies focus on removing single objects

One debris removal spacecraft removes one piece of debris

Often involves docking with debris and deorbiting using thrusters to deorbit
Laser Broom, Orion Project

Ground based lasers to vaporize debris to deorbit
Useful for smaller pieces of debris ranging from 1cm – 10cm

How about removing multiple dead satellites at a time?

ESA ClearSpace-1 & Debris Inclination Concentrations

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PROPOSAL: DRAG SAIL

Take advantage of the small amount of atmosphere in LEO

Though not much, there is still some atmosphere at 800km

Increasing cross sectional area using drag sails decreases the ballistic coefficient, increasing the decay rate
Can reduce decay time from centuries to a few years
Rendezvous and dock with debris object and deploy a drag sail

Drag Sail Deployment Test @ Purdue

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HAS IT BEEN DONE

Using drag sails to deorbit is not a new concept

It has been successfully tested with TechEd Sat 4

All concepts proposed involve equipping satellites with drag sails from the start to deorbit at the end of life
None involve attaching drag sails to debris already in orbit

This is the current proposal

Two methods

Single spacecraft equipped with multiple drag sails
Multiple spacecraft equipped with one drag sail each

It is achievable with today’s technology

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1. Launch

2. DRRAGS Spacecraft Rendezvous with Debris at 800km

3. Attach Drag Sail to Debris

4. Debris deorbits. DRRAGS remains in orbit at 800km

5. DRRAGS rendezvous with another piece of debris

6. DRRAGS attaches another drag sail to new debris object. Repeat steps 2 – 6 until ReDDDS runs out of drag sails to attach

Single Spacecraft

7. DRRAGS deploys its own drag sail at end of life

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SINGLE SPACECRAFT OPERATIONS

The single spacecraft approach works well with smaller, less massive debris objects 10cm – 100cm and m < 30kg

Smaller satellites, broken & free-floating pieces of a satellite

How will the drag sail attach to debris?

A net! This has been tested by ESA in zero-g for capturing objects. Works “extremely well”

How will the drag sail deploy?

Could be deployed completely passively using shape memory alloys
Shape memory alloy could be coated in high absorption, low emissivity material so it heats up into the desired shape upon exposure to the sun

No Sail	10kg	20kg	30kg
Very Long	5.2y	10.5y	16y

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CATCHING IN NET

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2. Deploy swarm of CubeSats

3. CubeSats disperse and rendezvous with different debris objects at 800km

4. Dock with debris and deploy drag sail. Initially use electric thruster to lower altitude by ~200km

5. Stow drag sail and undock from debris at 350km

6. CubeSat climbs back to 800km and rendezvous with more debris. Steps 3 – 6 are repeated until all propellant is expelled

7. Spacecraft deploys its own drag sail at end of life

1. Launch

CubeSat Swarm

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SMALLSAT/CUBESAT SWARM OPERATIONS

Intended for larger, heavier debris ranging from 100kg – 500kg

Dead satellites, empty kick stages, etc.

Much larger, non-disposable drag sail than single satellite

This is because debris mass is much higher

Heavier debris will require some assistance from the DRRAGS propulsion system

For a 14kg cubesat with an ion thruster, this uses about 5% of the propellant
Alternatively, if the target is still operational, it could use its remaining propellant to descend

8V Battery, 75W thruster, & four 3U 8W solar panels can provide enough power for the cubesat to climb back to altitude

This is assuming the cubesat uses its thruster for one orbit, and then recharges the following six orbits
For a 14kg CubeSat, the propulsion system provides 2.4km/s of dV
About 11% of the propellant is used to bring the cubesat back to 800km
40 weeks to return to altitude
This means it can make 5 trips total

No Sail	100kg	300kg	500kg
Very Long	36w	80w	124w

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SMALLSAT/CUBESAT SWARM OPERATIONS

How does the Cubesat dock with debris?

Extending a boom or tether with magnetic or elcectro-adhesive contact point
Currently being tested in space with Debris Removal Unprecedented Micro-Satellite (DRUMS)

How will the drag sail deploy?

The drag sail can deploy with the same mechanism as a solar sail
This has been demonstrated by with the LightSail2 cubesat

350km is the lowest the cubesat can go before atmospheric drag overpowers its propulsion system

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BENEFITS

Most of the technology has been demonstrated to some degree

Low thrust rendezvous

Northrop Grumman Mission Extension Vehicle

Shape memory alloy solar sail deployment laboratory test

NiTi tests @ Università di Roma-Tor Vergata in Italy

Catching debris in net zero-g test
CubeSat solar sail deployment
CubeSat docking to target
TechEd Sat 4 drag sail test

Removing multiple debris objects with one spacecraft is cheaper than removing one object with one spacecraft
Once the sail is deployed, the system is completely passive and self-stabilizing

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POSSIBLE ISSUES & CHALLENGES

Rendezvous with smaller debris has not been done

This must be demonstrated before DRRAGS can be employed

MMOD Strike is significantly higher due to the larger area

Small MMOD should shoot right through the sail, larger will absolutely obliterate it
However, hypothetical drag sail debris should decay quickly

Debris could explode and disable the DRRAGS spacecraft

If possible, pick debris with a low risk of explosion

Possible collision risk when descending through Starlink altitude, ISS altitude, etc.

Could possibly maneuver around potential collision threats

Possible challenge in stowing the Drag Sail in swarm concept

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QUESTIONS?