D rag and A tmospheric N eutral D ensity E xplorer

Drag and Atmospheric Neutral Density Explorer

Colorado Space Grant Consortium and

CU Aerospace Engineering Sciences

Meeting of the NADIR MURIOctober 21st, 2008Boulder, Colorado

2

DANDE - NADIR Seminar

Overview

1. Introduction2. Science3. Instruments4. The DANDE Spacecraft5. Program Status

3I - Introduction

The University Nanosat Program

• University Nanosat – The National Championships of Spacecraft Design– 2 year program in its fifth iteration– 10 out of 30 university proposals selected based on Air

Force Relevance– $85k initial seed funding for hardware and student

support– In January 2009, one school wins additional $85k, I&T at

Kirtland, and flight to Orbit• CU Nanosat Entry

– Has involved a core team of graduate students and expanded into 40 graduate and undergraduate students

– Many aspects of the ASEN Graduate Projects but organized as independent research and MS research

– Has leveraged over $240k from University, Department, DoD, and COSGC Funds

4I - Introduction

Nanosat V Program at CU

DANDE will improve atmospheric models and calibrate near real-time models by measuring the following

•Deceleration

•Atmospheric composition

•Horizontal Winds

DANDE is spherically shaped to minimize biases resulting from estimation of the drag coefficient

5I - Objectives and Requirements

DANDE – NADIR Synergies

• Provide the information to improve empirical models of neutral density• Determine the relationship between neutral density structure and satellite

drag• Understand the physical processes driving the variability of neutral

atmospheric density

6I - Introduction

Background and Motivation

Scientific understanding hindered by lack of neutral density, composition, and wind measurements

Precise orbit prediction depends on accurate knowledge of atmospheric density and in particular excursions from the mean state

drag induced drift

Relative Orbit of Two Separating Spacecraft

Storm response of CHAMP E/W winds

77

DANDE Science

wV

a

TV

ρ – density

Asc – projected area

Msc – s/c mass

CD – drag coefficient

scV

wV

a

TV

ρ – density

Asc – projected area

Msc – s/c mass

CD – drag coefficient

scV

8II - DANDE Science

Mission Statement

Mission StatementExplore the spatial and temporal variability of the

neutral thermosphere at altitudes of 350 - 200 km, and investigate how wind and density variability translate to

drag forces on satellites.

DRAG and

ATMOSPHERIC

NEUTRAL

DENSITY

EXPLORER

9II - DANDE Science

Objectives and Compelling Science Questions Addressed by DANDE

PO1relationship between total mass density, composition, and winds

Q1: What are the global relationships between density, composition and winds?

Q2: How do density, composition and winds vary with respect to each other locally?

Q3: How well do current empirical and first principles models emulate variations in density, composition and winds?

PO2relative contributions of density and winds to satellite drag

Q5: Under what conditions do winds have a non-negligible effect on satellite drag?

Q6: What is the relationship between spatial variability of density and winds, and the integrated drag on a satellite?

PO3key technologies

Q7: Can the in-situ density-measurement concept be employed effectively for aeronomic research within the framework of the University Nanosatellite Program?

PO4variation in coefficient of drag

Q8: How does the coefficient of drag vary when transitioning between free molecular flow and slip flow?

10II - DANDE Science

Objective Requirements

Measure in-situ density and composition (O:N2 ratio) during at least 5 sudden geomagnetic storms and 4 periods of quiet geomagnetic conditions in an altitude of at most 350 km and covering a minimum latitude of at least 54 degrees

Calibration and validation of models. Goal: also estimate the coefficient of drag in orbit at 350 - 100 km altitude.

Measure neutral winds at an altitude of up to 250 km and below and at latitudes of at least 54 degrees during 5 sudden geomagnetic storms and 4 periods of quiet geomagnetic conditions. Provide the wind data with a spatial resolution of at least 500 km (goal: 100 km).

Measure large-scale horizontal variations with in-situ density data over the course of at least 5 geomagnetic storms and 4 periods of quiet geomagnetic conditions

Develop a low-cost system to make in-situ measurements of the neutral atmosphere and adhere to Nanosat Program Requirements. Finish the proto-qualification unit on time and on budget.


Refs Requirement Precision(1-sigma)

Accuracy

absolute percent* absolute percent*

1.SYS2, 1.SYS52 Density 2x10-13 kg/m3 2% 1.0x10-12 kg/m3 10%

1.SYS6, 1.SYS7 In-Track Wind 100 m/s 20%** 100 m/s 20%

1.SYS56,1.SYS57 Cross-Track W. 100 m/s 10% 100 m/s 10%

1.SYS21

Composition Densities (O & N2) 7x1013 m-3 2% 5.3x1014 m-3 15%

1.SYS52,1.SYS72 Coefficient of Drag 0.1 5% 0.2 10%

*percent value based on average conditions during solar maximum, vernal equinox

**assuming a wind velocity of 1 km/s, storm conditions

Minimum Measurement Requirements

1.SYS26 , composition measurements with resolution of 1.5 m/Δm. Driven by 0.SYS1 and 1.SYS21(where m/Δm = half peak width at mass m)

horizontal resolution of 500km (~64s)


Wind and Density Requirement Relationship

Requirement

Goal

13II - DANDE Science 13

How Measurements are Made

• Identifying all components of the constituents of the drag equation.• With a near-spherical shape, an a-priori physical drag coefficient may be calculated and a physical density can

be obtained from the measurements

atmosphere

ρ - densityV

A

FD

CD

VW

aMVVACF WDD 2

2

1

accelerometersWTS sensor

a priori knowledge

tracking

a priori knowledge

a priori knowledge/ comparison

solutionmeasured

a priori

solution

solved

1414

DANDE Science Instruments

15III - DANDE Science Instruments

Accelerometers

Method to reduce this drift• Flip one accelerometer in positive and negative directions and remove bias• Modulate measurement to 6 μHz - 1 Hz range• 6 reduces the noise through averaging independent measurements by 0.41 (1/√6)• Provides redundancy

STAR accelerometer

Cost ~$3,000,000Precision 30 ngBandwidth 10 mHz – 100mHz

Cost ~$3,000Precision ng*Bandwidth 6 μHz – 10 KHz****must be able to reject the larger noise outside of 6 μHz - 1 Hz to achieve 79 ng

QA-2000 accelerometer

x 6


Accelerometer Measurement System

ANALOG FILTERING

A/D CONVERSION

LEAST SQUARES

70 ng1x100 1x1021x10-31x10-5

1.6x10-10

4.0x10-15

Frequency [Hz]

PS

D [

g2 /

Hz]

1.0x10-12

1x100 1x1021x10-31x10-5

1.6x10-10

4.0x10-15

Frequency [Hz]

PS

D [

g2 /

Hz]

1.0x10-12

spin rate

Low frequency bias


R

T

Problem Description: Measurement System

ACC-4

ACC-6

ACC-3 ACC-

2

ACC-

5

ACC-1

FD

PROCESS & AVERAGE

ω

AC

C-6

AC

C-2

AC

C-5

AC

C-1

AC

C-3

AC

C-4

ω = π/3 [rad/sec]


Accelerometer AnalysisLatitude [deg]

0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘ 0∘ 82∘ -82∘0∘

19III - DANDE Science Instruments 19

Wind and Temperature Spectrometer

CO

LLIM

AT

OR

ION

SO

UR

CE

DE

TE

CT

OR

AN

AL

YZ

ER

NMS302 POWER BOARD

NM

S303

DE

TE

CT

OR

BO

AR

D

-167 V

-100 V

e-

-3000V

T

NMS304 CONTROLLER BOARDNMS304 CONTROLLER BOARDNMS304 CONTROLLER BOARD

0V – 5V SCAN

5V

BU

S

I2C DATA BUS

-100 V -101 V

FARADAYCUP

IONIZER

TEMPERATURESENSOR

GROUND DEFLECTOR PLATE

HOT DEFLECTOR PLATE

BA

FF

LE (IO

N-D

EF

LEC

TO

R)

DIGITAL DATA ANALOG DATA

DE

TE

CT

OR

AN

OD

ES

15V BUS

Incoming Neutrals



1.Neutral particle (blue) enters the collimator. (Ions rejected)2.Neutral particle is ionized inside of a field free electron bombardment region3.Neutral particle enters the energy selector and undergoes acceleration towards the

exit 4.Outside the selector, the particle is accelerated abruptly by a -3kV potential towards

the Micro-Channel Plate (MCP)5.The impact on the MCP causes a cascade of electrons to travel towards one of the

anodes which measures the impact. Which anode is triggered depends on the angle at which the neutral particle entered the collimator.



Total number densities across all spectra as the satellite spins

-180

-155

-130

-105-80

-55

-30-520457095120

145

170

050

010

0015

0020

0025

00

WACC-4

ACC-6

ACC-3 ACC-

2

ACC-

5

ACC-1

ω

Angular position about the satellite spin axis, degrees

# of

par

ticle

s im

pact

ing

dete

ctor

Peak count of vertical distribution

~2000 counts

R

T


WTS Science Data Product Analysis

wind angle

N2 wind mag.

O wind mag.

O temp. N2 temp.



• Will meet science requirements and goals

•The error depends on the number of particles registered.•Determined for a true wind velocity magnitude W of 10 m/s:

Parameter % error*

Noise(Peak cts)

W T N(O) N(N2)

3%(1000)

13% 0.40% 0.55% 0.38%

1%(10,000)

5% 0.13% 0.18% 0.13%

*from Herrero et. al. unpublished work

DANDE


Wind and Density Requirement Relationship

Design


Density Error – Drag and Wind Data


Complex Geometry Effects

A behavior different from that of smooth spheres is observed for the faceted spheres. What is the physical drag coefficient of a faceted surface?

[Bowman & Moe 2005]

Starshine I

Physical CDP, 100% diffuse

Physical CDP, partly quasi-specular

Fitted CD

Expected fit


Results: Impacts on Starshine SurfacePercentage of Total Impacts

“longitude”

“la

titu

de”

2∘ x 2∘ bins

0.06 %

0.01 %


Drag Coefficient of DANDE

Bias induced by CD uncertainty using method of [Moe and Moe, 1996] at solar max

(2.216 - 2.118)/2.216 = 4.5%

2929

Spacecraft Engineering

30IV - Spacecraft Engineering

DANDE Overview

ESPA Ring DANDE Sphere

Lightband Adapter Bracket (LAB)

Baseline Configuration

18”

31IV - Spacecraft Engineering 31

Mission Timeline• Phase 1: LV Separation and

commissioning1. Launch Mode - time delay –

Safe Mode2. Full charge and checkout

[18 – 30 hours]3. Lightband jettison

• Phase 2: Attitude Acquisition1. Spin Up [24 h]2. Spin-Axis Alignment [120h]3. Reserve time [24h]

LV SEPARATION AND COMMISSIONING PHASE

Day 2Day 1

Wind

Composition

Acceleration

Tracking

Tracking

SCIENCE PHASE

DATA ACQUISITION1 orbit SCIENCE1 orbit STANDBY

DOWNLINK/UPLINK~2x in 24 hours

ATTITUDE ADJUST~1 orbit per day

RE-ENTRY DYNAMICS~LAST WEEK OF ORBIT

200 km – 100 km

Day 9 Day 100

• Phase 3: Science [~90 days]1. Science Mode2. Standby Mode3. Comm. Pass4. Attitude Adjust5. Repeat

32IV - Spacecraft Engineering

Spacecraft Layout

33IV - Spacecraft Engineering 33

–Spin stabilization about orbit normal• 40°/sec (10 rpm)• Only two maneuvers:

spin-up and axis alignment

–Sensors• Magnetometer for spin-up• Horizon Crossing Indicators for

spin axis alignment

–Actuators• 2x Torque rods: one along spin axis

and one transverse• Passive nutation damper

DANDE Attitude

3434

Program Status

35V - Program Status

Completed Formal Testing

TESTING


State of the DANDE Program: Hardware

HARDWARE & MANUFACTURING

Engineering Design UnitLessonsLearned Competition Review Hardware


Integration & Testing Schedule

Today Competition Review

38

Questions

dande.colorado.edu

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D rag and A tmospheric N eutral D ensity E xplorer

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