Preliminary Design of Preliminary Design of NEA Detection ArrayNEA Detection Array

Contractor 2Kim EllsworthBrigid Flood

Nick GawloskiJames Kim

Lisa Malone Clay Matcek

Brian Musslewhite Randall Reams Scott Wilkinson

Introduction

• An array of CubeSats will perform stellar occultation to discover and profile Near Earth Asteroids (NEAs) in the 40m to 140m diameter range.

• A optimal situation is discussed where there are unlimited resources provided, as well as a situation accounting only for resources that are available at this time.

Report Overview• Cartoon• Trade Tree• Formation Options• Telescope Options• Telecommunications Options• Propulsion Options• Chosen Formation

• Optimal Design• Limited Resources Design

• CubeSat Deployment• Launch Description• CubeSat Configuration• Cost Estimation

MISSION PHASELaunch-to-Orbit

Earth orbit to asteroid observation

Telescope

Dedicated launch vehicle

Piggyback on another spacecraft

TRADE TREE

Plus sign

YY Straightline

Plus sign

YStraight line

Refracting

Catadioptric

Cassegrain

Refracting

Catadioptric

Cassegrain

Telecommunications

Propulsion System

Satellite to Ground Station

Satellite -> Mother sat -> Ground Station

• What to send: Raw Data

Magnitude Profiles

Shadow Pattern

Cold Gas Thrusters

Electric Propulsion

Reaction Wheels

Formation OptionsFormation OptionsRectangular Plus Sign Plus Sign in Circle Z

Z in Circle

Empty Circle

X in Square

Asterisk

Triangle

YPeace Sign

Telescope Options• Refractive Telescope

+: High resolving power/image clarity-: Bulky, heavy, BIG!

• Catadioptric Telescope+: compact and portable; versatile because they use lenses and mirrors-: Secondary mirror can cause loss of light; image shift can occur if primary mirror is moved

• Cassegrain Telescope+: Secondary mirror effectively increases focal length; long focus increased image scale-: Stray light from the secondary mirror can wash out contrast; Mirrors are difficult to manufacture

Cassegrain System

• Image clarity is not an issue for this technology validation mission• Photodetector

• Cassegrains are compact enough to fit in a 2U CubeSat

• Launch with secondary mirror enclosed within the CubeSat, and extends once in orbit

Telecommunications Options

1. Send raw data from each satellite to the ground station

- Need a larger transmitter and antenna for each satellite

2. Send data from each satellite to a “mother” satellite which will transmit data to the ground station

- Send raw data- Create and send magnitude profiles from

each “eye” satellite as a function of x- Requires less power than sending raw data

- Create and send an interpolated shadow pattern- Requires less power than sending raw data- Requires a more powerful computer to perform

interpolation- Does not allow for multiple interpolations

Propulsion Options

• Propulsion System needed for attitude and orbit corrections

• Options1. Cold Gas Thrusters

- Small size (will fit inside 1U) - Pressurized gas also used for telescope arm extension

2. Electric Propulsion - Larger size, more complex, and expensive- Requires more power then the other options (larger solar panels)

3. Reaction Wheels - Large and more massive then the other propulsion options - Can not preform delta-v maneuvers only attitude corrections

Optimal Design

• We first devised a configuration with a resolution of 10 pixels for the smallest shadow, for the 140m asteroid, but also capable of capturing the silhouette of a 40 meter asteroid.

• This means we had to have one telescope for every 67 meters, and to see an entire 40 meter asteroid at the same resolution, we needed 22 telescopes perpendicular to the motion of the asteroid’s shadow.

• We assumed that the center of the shadow would pass through the center of our configuration.

Optimal Design

x

120°

We chose the Y formation, since it requires the least amount of telescopes but still has the required resolution.

x + x*sin(30°) = 22x = 15

So each arm would have 15 CubeSats, plus one central communication satellite (launch vehicle), for a total of 46 satellites.

Limited Resource Design

• It’s possible that, due to cost restraints, we could be limited to 12 CubeSats

• In order to accomplish the minimum number of pixels, we are forced into a line of 12 CubeSats

• This results in a less-than-ideal resolution

Limited Resources Design

Satellites will expand and contract for varying sizes

For 40m asteroid Δy = 228.40mFor 140m asteroid Δy = 78.11m

CubeSat Deployment

Launch Logistics

Launch Vehicle Inside View, Launch Vehicle

CubeSat Configuration

• Pressurized gas from propulsion system used to deploy arm.

• Extends 10cm outside of the CubeSat.

• Max Primary Mirror Diameter is 10cm

Preliminary Cost Estimates• Assumed $33,000 per kilogram

• Assumed price of Launch Spacecraft to be $800,000

• Assumed price of Cassegrain telescope to be $3000 each

Cost-Constrained

Ideal

Design Advantages• Chosen formation minimizes number of

satellites needed to occult from all angles• Minimizes mass of individual CubeSats by

using Cassegrain telescopes with extendable arms

• Dedicated launch vehicle: does not depend on the capabilities of another spacecraft to reach the correct formation

• Smallest, lightest weight propulsion system. Allows for attitude and orbit corrections

• Telecommunication option reduced overall mass while ensuring communication redundancy