Earth from Space, 3rd Int. Conf., Dec. 4-7, 2007, Moscow, Russia > Dr. R. Sandau > 1 Small Satellites for Earth Observation Prospects & Limitations Rainer

Earth from Space, 3rd Int. Conf., Dec. 4-7, 2007, Moscow, Russia > Dr. R. Sandau > 1

Small Satellites for Earth ObservationProspects & Limitations

Rainer Sandau


OUTLINE

1. Why small satellites? 2. Small sat missions: Facts & Trends3. Application requirements4. Restrictions5. Future of small satellite missions6. Conclusions


1 M$ 10 M$ 100 M$

cost

1 yr 2 yrs 5 yrs

response time

examplesCubeSat: 1 kg, ca. 2 yrs, 0.2 M$

ENVISAT: 8 t, 15+ yrs, 3 × 109 $

mass

1 kg 10 kg 100 kg 10 000 kg

Pico Nano Micro Mini

Small Satellites Large Satellites

1000 kg


Why Small Satellites

Classification parameters

Mass/Volume

Costs

Preparation time

have large influence on

Launch costs

number of opportunities

adoption of new applications

temporal resolution (through constellations)

reliability/continuity (replacement)


The advantages of small satellite missions are:

more frequent mission opportunities and therefore faster return of science and for application data

larger variety of missions and therefore also greater diversification of potential users

more rapid expansion of the technical and/or scientific knowledge base

greater involvement of local and small industry.


Small satellite missions are supported by several contemporary trends:

Advances in electronic miniaturization and associated performance capability;

The recent appearance on the market of new small launchers (e.g. through the use of modified military missiles to launch small satellites);

The possibility of ‘independence’ in space (small satellites can provide an affordable way for many countries to achieve Earth Observation and/or defense capability, without relying on inputs from the major space-faring nations);


Earth Observation Request (1)

1

2

3

4

5

6

7

8

9

100m 10m 1m 0,1m 0,01mgeometrischeAuflösung

1

2

4

5

3

8

7

6

9

1

2

3

4

5

6

7

8

9

100m 10m 1m 0,1m 0,01mAuflösung

1

2

4

5

3

8

7

6

9

GSD

Sp

ectr

al R

esol

uti

on

Pan

chro

mat

ic

Mu

ltis

pec

tral

Hyp

ersp

ectr

al - Hydrology

- Agriculture

- Ressource Monitoring

- Environmental Monitoring

- Forestry

- Intelligence Services

- Urban Development

- Topography

- Traffic


Earth Observation Request (2)

1

101

102

103

104

105

1

1 year

10 years

1 10 100 1.000 10.000

Rev

isit

Tim

e [h

]

geometrische Auflösung [m]

1

5

- Kartographie

- Geologie

2

6

- Forstwirtschaft

- Ozeanographie

3

7

- Landwirtschaft

- Hydrologie

4

8

- Naturkatastrophen

- Meteorologie

1

2

3

5

6

48

7

1

101

102

103

104

105

1 day

1 month

1

10

1 10 100 1.000 10.000

ösung [m]

1

101

102

103

104

105

1

1

10

1 10 100 1.000 10.000

[m]

1

5

- Mapping

- Geology

2

6

- Forestry

- Oceanography

3

7

- Agriculture

- Hydrology

4

8

- Disaster Monitoring

- Meteorology

1

2

3

5

6

48

7

GSD [m]


Optical Small Satellites

Ground Resolution Spectral Resolution Temporal Resolution

Increasing

Example: Eros-B/PIC-2Launch 25.04.2006Mass 350 kgGSD 0.82 m

Increasing

Example: Proba/CHRISLauch 22.10.2001Mass 149 kgHyperspectral Imager

Unique opportunity for affordableConstellation

Example: DMC-1Daily global coverageGSD 32 mSwath 600 km


Instrument & platform requirements

Optical P/L

High res imaging

GSD optics downlink

Stat. Dynam. construction Data rate & volume

MTFradiometry

MTFpointing

Massvolume

Antenna sizepower


Radiometric aspects

Example orbit: H=600km, vground 7km/s

GSD = 10 m tdwell 1.4 ms

GSD = 1 m tdwell 0.14 ms

tdwell(1m)/tdwell(10m)=1/10

IFOV(1m)/IFOV(10m) = 1/100

For good signal and SNR

- TDI with N stages N • signal, • SNR (IKONOS, EROS-B)

- Slow-down mode (EROS-A1)

N


Spatial Resolution

MTFSR = MTFOptics • MTFD • MTFLM • MTFJ

tint < 0.2 tdwell J < 0.1 x

MTFSR = MTFstatic/instrument • MTFdynamic/platform

sin ( )LM xc a k

sin ( )LM xc a k

2 2 2exp( 2 )J Jk


Spatial Resolution

0 0.5 10

0.5

1

Normierte Ortsfrequenz

MTFr1 i

MTFr2 i

MTFdi

f i

0 0.5 10

0.5

1


MTFa1 i

MTFs2 i

MTFr2 i

MTFdi

MTFpf i

MTFpf1i

f i

0 0.5 10.5

0

0.5

1


MTFdi

MTFs1 i

MTFs2 i

f i

MTFdi MTFa1

i MTFa2

i MTF1

i MTF2

i

0 0.5 1

0

0.5

1


MT

F v

on B

eweg

un

g u

m G

SD

x 0

.2, 1

, 1.5

1

0.30

MTFa1 i

MTFa2 i

MTFa3 i

10 f i

MTF: LM = 0.1, 1, 1.5 ∙ GSD MTF Detector, Jitter = 0.1, 1 ∙ x

MTF Detector, Sinus vibration a = 0.1, 1 ∙ x Total MTF with LM = 0.2 x, = 0.1 x, a = 0.1 x, Detector-size x


Pointing stability

From 600 km orbit, GSD = 1 m IFOV 1.7 rad 0.3 arcsec

Drift < 0.2 IFOV 2.4 mrad/s 8 arcmin/s

For TDI with N = 96 25 rad/s !


Future of Small Sats for Remote Sensing

New capabilities

the convergence of data acquisition and data visualization technologies

the ready availability of new small launchers and the rise of “space tourism”

the development of smaller, lighter, lower power satellites that can act as a constellation or independently


Convergence of data acquisition and data visualization technologies

Example:

NASA’s “A Train” (Aqua, CloudSat, CALIPSO, PARASOL, Aura, and OCO)

+NDVI small sat for crop yield forecasting in a particular region,

Aerosol and cloud correction using data from the A Train.


Small launchers & „Space Tourism“

Getting into space is still a challenge and costly

During the last 10 years more small launchers at prices reasonable compared to the cost of a small sat (e.g.NASA/DLR GRACE constellation with

EUROCKOT, SS-19 ICBM)

New impetus of „space tourism“ (Oct.4th, 2004, Burt Rutan & Paul Allan win the AnsarX PRIZE)

Looking back: At the turn of the last century, air travel was relatively risky and quite expensive.

Now we fly e.g. apples half way around the world at prices that are competitive with local transport & production.


Conclusions

Developing Small Satellites for Remote Sensing is within the means of many nations

They provide enormous opportunities :•To do more with less•Address local and global needs•Provides an affordable means to improve the temporal resolution•Focus the development of the technical infrastructure of a country•Reduce risk in the use of space


BIRD Payload Segment

Mass of s/c: 94 kg

Mass of p/l: 30.2 kg

WAOSS-B MWIR TIR Wavelength 600-670nm

840-900nm 3.4-4.2µm 8.5-9.3µm

Focal length 21.65mm 46.39mm 46.39 mm Detector CCD CdHgTe CdHgTe Ground pixel size 185m 370m 370m Ground sampling distance

185m 185m 185m

Swath width 533km 190km 190km 1 at 572km Orbit altitude


Fire detection by MODIS and BIRD (Australia, January 5, 2002)

MODIS: Fire map BIRD: Fire map


F = 1.2 x = 10 m

Nyquist frequency

optics

spatial frequency (cy/mm)

Documents

Earth from Space, 3rd Int. Conf., Dec. 4-7, 2007, Moscow, Russia > Dr. R. Sandau > 1 Small Satellites for Earth Observation Prospects & Limitations Rainer