twentesat mission...twentesat slide : 2 goals of my talk • tell you about space missions •...

TwenteSat Slide : 1

TwenteSat mission

Mark BentumUniversity of Twente – EWI/TE/SRR

ASTRON

[email protected]

TwenteSat Slide : 2

Goals of my talk

• Tell you about space missions• Explain why (ultra) low frequency astronomy

is very interesting• Why this has to be done in space• Why small satellites can do the job• Tell you about our plans ….

TwenteSat - Building the first UT Satellite

• Discuss next steps.

TwenteSat Slide : 3

Introduction

The first artificial satellite was Sputnik 1, launched by the Soviet Union on October 4, 1957, and initiating the Soviet Sputnik program, with Sergei Korolev as chief designer.

This in turn triggered the Space Racebetween the Soviet Union and the United States.

TwenteSat Slide : 4

History • Space race driven by superpowers.• Lots of know-how and money required.• Eventually other countries joined in, often

as a matter of national prestige.• Science & exploration from early on.• Communications satellites primary early

commercial driver.• With weather, mapping, etc., line is

blurred between commercial and scientific endeavors.

• Now, some of the fruits are free – e.g. Google Earth.

TwenteSat Slide : 5

Very interesting documentary

• Race For Rockets(1944–1949)

• Race For Satellites(1953–1958)

• Race For Survival(1959–1961)

• Race For The Moon(1964–1969)

TwenteSat Slide : 6

Current Situation• A new space race is on, with many governments playing,

often as teams. • Science & exploration missions continue, but with a new

emphasis on efficiency. No longer “succeed at all costs.”• Some space systems in dire need of replacement.• Seem more willing to accept disruptive technologies by

using the latest “new thing” – trying to keep up with the rapid pace of technology.

• No longer an isolated industry – lots of new players (Virgin Galactic, SpaceX, Rutan, etc.) in new markets.

TwenteSat Slide : 7

Who Uses Space?• The usual suspects

– Military– Commercial– Science & exploration

• The new kids on the block– Tourists– Prize seekers– “New Pioneers”– Educators– Data gatherers– The usual suspects, trying to invigorate their people,

processes, profile, etc.

TwenteSat Slide : 8

Fundamental Changes?

• Large, expensive satellites won’t disappear any time soon.

• For small satellites, access to space is increasingly a matter of simply showing up at the right time with the right amount of money. The door is open, and you have many doors to chose from.

• The “FedEx satellite” has become a reality.• For small satellites, space is definitely open

for business. And science, too. And education. And …

TwenteSat Slide : 9

CubeSat

• In 1999, California Polytechnic State University and Stanford University developed the CubeSatspecifications to help universities worldwide to perform space science and exploration.

• Usually has a volume of exactly one liter (10 cm cube), weighs no more than 1.33 kilograms, and typically uses commercial off-the-shelf electronics components

TwenteSat Slide : 10

Why CubeSats?

• Level of technology entirely manageable.• “Arrive and orbit” means no previous experience required.• Timelines, success rates, costs incurred, data collected, etc.

from previous missions all point to manageable projects with results in 2-5 years.

• Highly interdisciplinary:– Electrical, mechanical, computer & systems engineering– Communications– Program management– And more …

• Low per-mission costs.• Regional / global communities.• Failure is not catastrophic.


What Usually Happens?• Someone gets excited about an idea.• Idea turns into a CubeSat mission proposal.• Choose launch opportunity. This sets the timeline.• Realize all the different aspects of a successful mission

program. Recruit friends from academia & industry. Offer students pizza.

• Obtain funding (the hard part). Beg, borrow, steal.• Move through PDR, CDR, etc. to complete the CubeSat.• Deliver CubeSat for integration.• Cross fingers on launch date.• Celebrate!


Why are we interested?

• We (at least I) have an interesting science mission.

• We have the technology and (most of) the knowledge to really build a (small) satellite.

• Building a satellite can be a very interesting large student project, which can be helpful for your future career and for the PR of the UT.

• And to be honest: don’t we all like somethingflying around the Earth with our name on it ??


Science mission

• Astronomy

• After 400 years: new oppertunitieslow frequency radio astronomy


Science: Dark ages

• The highly red-shifted 21 cm hydrogen line is the only known way to observe the dark ages

• At that time the universe was filled with neutral hydrogen and opaque to visible light

• Neutral Hydrogen absorbsphotons and re-emit themin random directions

• During the “epoch of re-onization” new stars ionized the hydrogen and the universe became transparent again. (~400 million years after the BB)


Science: Transient radio sources

• Solar and planetary radio bursts• Extra solar planets• X-ray binaries


Science: Ultra-High Energy particle detection

• Extreme high energy• Problem: there not so many

• Perhaps the Moon can act as a detector.• Hitting the Moon will cause a particle shower,

detectable at low frequencies.

(Perhaps also the detection of Neutrinos. However, they will hit the Moon deep in the surface … low frequencies might detect it…)


Low frequency radio astronomy


Low frequency radio astronomy• Problems:

• Atmosphere not (fully) transparant below 30 MHz,

• Interference on Earth to large

Need for a space segment to augment LOFAR sensitivity at low frequencies

Space segment required anyway for frequencies below 20 MHz

NASA launched RAE-1 into Earth orbit (1968)

• Discovered the ionosphere is highly active

• Earth emits very strong Kilometric Auroral Emissions RAE-1


Specs

• RAE-1 (Explorer 38) – 1968 July 4 – 190 kilogram– Earth orbit

• RAE-2(Explorer 49)– 1973 June 10– 328 kilogram– Moon orbit– 25 kHz to 13.1 MHz


Second attempt – RAE-2

RAE-2Source: J.K. Alexander et al. (1975)


RAE-2 results• Extremely poor angular resolution: Angular resolution ~30°

• Strong diffuse Galactic emission

RAE-2 observations at 1.3 and 9.18 MHz,

Novaco & Brown,

1978


Our vision:OLFAR

• Nano/small satellites• Formation flying• Deployable antenna for the frequency band between 1

and 30 MHz• Ultra-low power receivers• Intra-satellite communication• Autonomous distributed processing• Using diversity techniques for downlink

A Nano-Satellite Swarm for

Radio Astronomy


Satellite concept

wavefront

aperture array:beamforming and/or

correlation

centralizedcorrelation,centralized

transmission(option)


Relevant Space missionsSome relevant space missions

• Delphi - C3 Nanosatellite student project, Delft University, Nl, 2008

• YES2 Technology demonstration satellite (e.g. tethers), ESA, 2007

• SMART-1 Moon (a.o. water) mission, ESA, 2003-2006

• Cluster-II Four satellite magnetosphere mission, ESA, 2000

• FORTE NASA, Fast Transient Events, 800 km Earth orbit, 1997

• WIND Magnetospheric and ionospheric studies, NASA, 1994

• Waves @WIND Radio and plasma wave investigation

• RAE Low frequency mission, Moon orbit, NASA, 1973

Space missions, planned

• Swarm Earth satellite cluster, geo magnetic field mission, ESA, concept study

• MoonLITE Moon mission, concept study

• DARWIN Four or five satellites searching for extra solar planets, ESA, planned

• SMOS Soil moisture and ocean salinity mission, ESA, scheduled 2009


Signal processing architectures

rawtransmission

centralizedcorrelation

distributedcorrelationdistributed

transmission

ring distributed

correlation

distributedcorrelationcentralizedtransmisson

signal processing and imaging principle: narrow band correlation and all-sky imaging


Communications scenario

Schematic diagram of the downlink ISL.

Uplink and downlink between the array and EarthInter satellite link (ISL) between the individual nodes of the arrayIntra satellite communication of parts of the satelliteReceiving antennas for radio astronomy purposes.


•Depends on deployment locations:

– Earth-leading or trailing• Permanent observations are possible

– Earth-Moon L2• Permanent observations possible• Requirement for radio-silence on the far-

side of the moon difficult to uphold, given the need for relay-satellites in lunar orbit

– Lunar orbit• Limited observation time due to low duty

cycle of the system, depending on orbital altitude

• (Duty cycles ranging from 4.8%-25%)

Downlink Communication


•Ground station antennas assumed to be large (ø10 m), and dedicated

•Phased Array panels used on all satellites– Panel sizes are 9 x 9 cm– Limited beam steering used

• Earth is at most 1.9° in size

– 2 deployed configurations analysed: • 3 x 1 panels on either side of the satellite (6 panels in

total)• 3 x 3 panels on either side (18 panels in total)

Downlink Communication


Link budgets (example)

k


Antenna concept

Antenna types considered:• Dipoles (two)• Tripoles (a misnomer, three dipoles are

meant)• Monopoles in a tetraeder configuration• Magnetic loops


Satellite system

• Mechanics and system engineering• Absolute and relative navigation and attitude• Inter-satellite link• Active antenna system for low-frequency radio astronomy• Sensors for relative attitude determination• Star trackers for absolute attitude determination• Constellation maintenance• Correlation software and hardware• Overall observation control

LNA Filter A/DPre

processing

Corre-lationInter satellite link

D/A

Upconvert and send to Earth


Preliminary specifications

1 MHzInstantaneous bandwidth

Confusion limitedSensitivity

1 sSnapshot integration time

Diffraction limitedSpatial resolution at 1 MHz

1 kHzSpectral resolution

Formation flying, investigate 2-D and 3-D

Configuration

between 100 kmMaximum baseline

50Number of antennas / satellites

dipole, also investigate tripoleAntennas

1-10 MHz, goal 0.3-30 MHzFrequency range


Example – Delfi-C3 Cubesats


Step 1 : TwenteSat

• Build the first interferometer in Space, so …two satellites operating together !!– Two receivers– Intersatellite communication– Link to Earth

• First study of suitability of low frequency radio astronomy in space.

• Answers to currently unknown questions wrt. The ionospere and RFI. Might be very helpfulfor future missions.


Issues

• Space-segment– Command and Data Handling (C&DH) System – Communications system and antennas – Electrical Power System (EPS) – Propulsion – Thermal control – Attitude Control System (ACS) – Guidance, Navigation and Control (GNC) System – Structures and trusses

• Payload• Ground-segment• Related issues

– Documentation– PR– ...


Construction of the satellite

• Team areas / assignments– Software– Electronics– Structures / Mechanics / Thermal– Communications & GS– Power– Documentation / Web– Project Management

• Clear documents (e.g. pin allocations on bus) are a requirement

• Team-based approach, with regular oversight and mentors’ meetings


Integration & Launch

• Luckily for the builder, this stage of the mission is beyond your control!

• You:– Ensure your CubeSat meets the CubeSat specifications– Send it to your integrator (e.g. ISIS)– Wait for launch– If possible, send team to launch site in order to observe &

learn

• Launches are often delayed. You should be prepared for this, with procedures to (re-)charge batteries while in storage, verify functionality, even update software fix bugs.

• Launch is risky! Rocket may explode!


Idea

Receiver-1

Receiver-2

Tether


Some system aspects

• Antenna design for 1-30 MHz band• Active LNA • Receiver – filtering, sampling,• Timing, clocking (local and global)• Localization (using tether information)• Digital signal processing

– RFI mitigation– Filtering– Subband sampling– Distributed correlation, tied-array calculations

• Data transport– Between individual nodes– Corrrelated and/or tied array data to datacente

• Use of spatial diversity techniques?

• Datahandling– Groundstation– Storage– Post-processing– Calibration


And now ….

• Interested people gather• Make teams / project leader / team leaders• Make good plan

• Training by experts from ISIS

• Action….• Ready in ~ 2 years

twentesat mission...twentesat slide : 2 goals of my talk • tell you about space missions •...

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