EUSO – BALLOON
MISSION SPECIFICATIONS
EUSO-MS-INST-402-IRAP V2.0
EUSO-BALLOON MISSION SPECIFICATIONS
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Prepared by
Peter von Ballmoos (IRAP)
with the participation
of the JEM-EUSO collaboration
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23/11/2012
27/11/2012
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Guillaume Prévot (APC)
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Peter von Ballmoos (IRAP)
27/11/2012
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Language : EN
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Brief description
EUSO-BALLOON
MISSION SPECIFICATIONS
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1 Scope of the Document
This document describes the high-level mission specifications of the EUSO-BALLOON experiment. The
instrument technical specification and the design of the instrument are defined to be compliant to these
requirements.
The balloon mission definition will be based on these requirements.
This document is part of the EUSO-BALLOON documentation for the CNES End-Of-Phase-A review in
January 2012.
A short description of the scientific goals of EUSO-BALLOON is given in Sec. 3. The science and
operational requirements deriving from the science goals are described in Sec. 4 and Sec. 6 respectively.
2 Applicable documents
[RD1] "La mission JEM-EUSO", Proposition pour une participation française, APC/CNES, décembre 2008
[RD2] The JEM-EUSO purple book v. 2010
3 Acronyms
DD = Definition Document
EUSO = Extreme Universe Space Observatory
EAS = Extended Air Shower
JEM=Japan Experiment Module
TBC = To Be Confirmed
TBD = To Be Defined
TBW = To Be Written
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4 Mission Objectives
EUSO-BALLOON is a pathfinder balloon mission for the Extreme Universe Space Observatory on-board
the Japanese Experiment Module (JEM-EUSO) mission. Hosted on the Japanese Experiment Module of
the ISS by 2017, JEM-EUSO is designed to identify the astrophysical origin and nature of the ultra high
energy cosmic rays, the most energetic particles known in the Universe.
The objectives of EUSO-BALLOON are
(1) to perform a full end-to-end test of a JEM-EUSO qualification model consisting of all the main
subsystems of the space experiment,
(2) to measure the critical atmospheric and terrestrial UV background components,
(3) to perform the first detection of air-showers by looking from above the atmosphere.
Scientific objectives of JEM EUSO:
The Earth is being continuously bombarded by high-energy cosmic rays. While cosmic rays with energies
up to 1017 eV are thought to originate from objects in our own Galaxy, such as from the expanding
shocks of exploded stars, understanding the origin of the still mysterious highest energy cosmic rays with
energies >5.1019 eV is one of the great challenges in astrophysics.
Ultra-high energy cosmic particles may be protons, nuclei, photons, neutrinos or possibly new particles
with energies ranging from a few 1018 eV to beyond the decade of 1020 eV, i.e. at the very end of the
known spectrum. The acceleration of the latter ultra-high energy particles involves the most extreme
physical conditions in the Universe, either in known, but poorly understood, or yet unknown
astrophysical sources, possibly involving new physics and new astrophysics.
These ultra-high energy cosmic rays are very rare (only around 1 per square kilometre per millennium!).
Less than a dozen of such events have been detected so far using different ground-based air shower
detectors in the past 30 years. Although hints for some correlation with Active Galactic Nuclei has been
presented, up to now there has been no convincing identification of any of these events with a likely
astronomical source, even though the deflections of these particles are expected to be small at such high
magnetic rigidities.
The exact nature of the UHECRs is also unknown, although data point to an hadronic composition of
protons or heavier nuclei.
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With the goal of pushing forward the intense research activity developed on the ground around the
mystery of UHECRs, JEM-EUSO, the first space mission devoted to this fundamental question, will
observe the extensive air showers induced by the UHECR's interacting with the Earths atmosphere from
above, with unprecedented acceptance and integrated exposure.
For a comprehensive description of JEM-EUSO and the science case of EECR please see "La mission JEMEUSO" [RD1] and the JEM-EUSO purple book [RD3].
Objectives of the balloon flights:
EUSO-BALLOON will serve as an evaluative test-bench for the JEM-EUSO mission as well as any future
mission dedicated to the observation of extensive air shower from space. Through a series of
stratospheric balloon flights, the following objectives shall be attained:

A-level (technology demonstrator): Full scale end-to-end test of all the key technologies and
instrumentation of JEM-EUSO detectors. Particularly, crucial issues that will benefit from the
balloon flights include the HV power supplies, the HV switches (HV relays commuting the HV in
case a city or a bright atmospheric event comes into the FOV and on a pixel), the Front-End
Electronics (including the ASICs and FPGA), the onboard hardware and software algorithms
involved in the triggering and recognition of cosmic-ray initiated air showers.
In this context all key French contributions, from the ASIC performance to the calibration and tests
of the Focal Surface detectors will be performed and field-tested in the EUSO-BALLOON flights.

B-level (cosmic ray acquisition and background study): Although the physics and the
detection technique is well established and daily used in ground detectors, the observation of an
Extended Air Shower (EAS) from space through the UltraViolet (UV) light emission has never been
performed previously1. Observation of EAS from space for the first time will confirm the feasibility
of the technique and provide valuable data for all future space-borne UHECR experiments.
Since JEM-EUSO uses the Earth’s atmosphere to observe UV (300-400 nm) fluorescence tracks and
Cherenkov reflections from EAS, the instrument is sensitive to the variation of the background
sources in the UV range. Measuring the background light / airglow in the near UV region is
1Although
a number of background measurements have been done, even from space, no
focusing instruments have been employed and, most importantly, spatial resolutions (“pixel
size”) on the ground were much larger. Large localized background signals could have been
washed out by the integration over a large surface, and likewise, possible temporal variations on
small scales were not known/constrained. It is therefore important to better understand the
background in the same conditions as JEM-EUSO will experience.
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therefore an important goal to successful operation and optimization of the working mode of the
JEM-EUSO mission. The main objectives are thus:
- experimental confirmation of the effective background below 40 km observed with a pixel size on
ground representative for JEM-EUSO (116 m in case of +/-4 deg FoV).
- acquisition of 2.5 microsecond frames of UV signal and background (in a format similar to JEMEUSO) from a balloon-borne gondola
- testing of the observational modes and switching algorithms.
- testing/optimization of the trigger algorithms with real observations and changing background.
- testing/optimization of the trigger algorithms with real observations above various ground
surfaces.
- testing of the acquisition capability of the IR camera (TBC)

C-level (precursor mission) :
- First detection ever of air-showers by looking downward from the edge of space2.
- detection of laser induced events from space (TBC).
5 Payload Overview
EUSO-BALLOON will consist of a focal plane detector made from a single PDM (Photo-Detector Module,
composed of 36 multi-anode photomultipliers containing 64 anodes, with associated ASICS, HV and HV
switches) representing 2,304 pixels, and a single Fresnel Optics made from 2 PMMA square lenses (UV
transmitting polymethyl-methacrylate). The 15 x 15 cm focal plane and the 100 cm x 100 cm Fresnel
lenses provide a field of view of ± 4° and shall observe in “nadir mode” that can be varied during later
flights in a range between 0° to 30°(TBC).
2
if the TUS mission will be launched in 2012, the EUSO-Balloon might not be the first experiment
to observe EAS from space, but first from a balloon platform. The first detection will be
guaranteed if we could accumulate several nights of flight. According to our estimation we can
get 2-3 events/night at E > 2.1 1018 eV, this threshold energy arising from the background value
measured by Yoshiya et al…However if the background is 2 times higher, the energy threshold of
the detector is also 2 times higher as an example, the event rate will be less than 1 ev/night.
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Integrating the Fresnel lens as a port-hole window directly into a watertight telescope structure will
make the crucial payload elements (PDM, electronics) entirely water tight without moving parts and will
permit offshore recovery. During a first flight (nadir pointing), this spin rate will be determined by the
natural azimuthal oscillations of the flight train. For later flights, the inclination of the pointing axis will
be controlled (jack & 5th strap) between 0 and 30° w/r to the nadir and an azimuth motor will provide the
possibility to perform revolutions with a spin rate of up to 3 rpm. Performing azimuthal revolutions will
simulate a groundspeed comparable to the ~ 7 km/s of the space-station. Attitude information is
obtained from a differential GPS system. In order to monitor the actual cloud covers, a co-aligned IR
camera will observe the FOV from a second port-hole. A possible option to create signal-type events is to
use an onboard laser for simulating air-showers within the field of view.
Fig. 1: possible concept of the instrument/gondola with floater-crashpads during a first flight (nadir
pointing)
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Fig. 2: Schematic of the instrument configuration in a watertight telescope envelope
Fig 3 : During later flights, the inclination of the pointing axis w/r to the nadir and azimuthal revolutions
will simulate a groundspeed comparable to the ~ 7 km/s of the space-station.
The total suspended mass (including batteries, watertight telescope structure, gondola) is expected to
be less than 200 kg (TBC) while the dimensions of the gondola-capsule are expected to be within 2 m3.
Besides a TM & TC system with the highest data rate available in 2013 (by default NOSYCA, L band ,1.5
GHz see AD4) on-board data storage of an higher amount of data is required to guarantee maximum
return from the flights.
6 Science requirements
The main scientific requirements (SR) for the three levels of the mission objectives (presented in section
4) are summarized below:
A-level (technology demonstrator):
[SRA1] A payload representative of JEM-EUSO shall be made to work at a float level above 40 km and
take data in low background conditions, as well as in intense background conditions caused by artificial
background.
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[SRA2] After each flight, the payload shall be recovered for further tests/flights.
B-level (real data and background study) :
The acquisition of real flight data with an instrument of the JEM-EUSO type has never been performed
previously. All estimates and simulations are based on extrapolations from ground systems, from a few
data points of non-imaging balloon systems and from theoretical models. Since JEM-EUSO uses the
Earth’s atmosphere to observe UV (300-400 nm) fluorescence tracks and Cherenkov reflections from
extensive air showers, the instrument will be extremely sensitive to the slightest background sources.
Measuring accurately the BG light / airglow in the near UV region is therefore an important facet for
operating the JEM-EUSO mission.
The B-level requirements for EUSO-BALLOON consist in measuring background levels over different
surfaces (land/ocean) and with different illumination (moon/moonless). While a part of thess
requirements may already be met during a first balloon flight (together with A-level engineering goals),
a second balloon flight shall fill in the remaining B-level requirements.
[SRB1] acquisition of JEM-EUSO type data, test the trigger algorithm performances. Priorities for
collecting data are in descending order :
1st priority : over ocean / moonless [SRB1a]
2nd priority : over ocean / moon [SRB1b]
3rd priority : over land / moonless [SRB1c]
4th priority : over land, moon [SRB1d]
Each pixel of the PDM will be calibrated absolutely in efficiency with a precision better than 2%. The gain
of pixels will be adjusted within 1%. We therefore want to experimentally confirm the effective
background below 40 km, perform the acquisition of JEM-EUSO type data, and adjust the trigger
algorithms with real data.
As the modelling of the EECR tracks in JEM-EUSO requires knowledge of the cloud cover and altitude,
and IR camera shall be operated :
[SRB2] Operation of an Infrared Camera to measure temperature/altitude of cloud cover.
C-level (precursor mission):
The goal is to perform the first detection of air-showers by looking downward from the edge of space.
The atmospheric showers that can be observed by EUSO balloon have an energy E of ~ 2-3 1018 eve
(TBC). The rate of such events is estimated to be 0,1 ev/h TBC.
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[SRC1] Detection of several (≥10) representative Cosmic Ray events.
The measured information must be representative for the parameters measured by JEM-EUSO, i.e they
must be performed from a sufficiently hight float level, (above 40 km during the first nights and above 35
km after 3 nights) to include as much airglow as possible. As in JEM-EUSO the temperature/altitude of
the cloud cover has to montiored during the flight. Also, the chances of detecting a small number of
Cherenkov albedo's of the air-showers shall be optimized. In order to have a "contingency sample" of
representative events, artificial (flasher/laser) events shall be created within the field of view of the
instrument.
7 Mission Requirements
The above science requirements (SR) translate into the following mission requirements (MR) resulting
from
A-level mission requirements
[MRA1] Accommodate a payload representative of the basic JEM-EUSO acquisition module
(Photodetector module + Cluster Control Board) and which includes an optical system. Also, all HV
(switch) systems must be able to work in vacuum i.e. at a 3 mbar float level.
[MRA2] flight data recording at float level over land is expected to last at least 3 (TBC) hours during a
moonless part of the flight, and 3 (TBC) hours during a moonlit phase (<25 (TBC) % full).
The absolute minimum requirements for a first flight are 2 hour (TBC) during the night with a less than
(<25 TBC %) full moon.
[MRA3] flight data at float level shall include sudden background enhancements due to city lights etc…
[MRA4] The instrument must be built as to withstand landing and (late) recovery at sea, or a landing
with 1 parachute au of 3.
B-level mission requirements
[MRB1] A second balloon flight shall fill in the B-level requirements [SRB1] that were not achieved in a
first flight. As the first priority is [SRB1a] - the launch site/season will be chosen to allow for a flight over
an ocean, the precise launch date shall allow to observe at least 2h (TBD) at a float level of 3 mbar.
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[MRB2] Testing the operation of a prototype Infrared Camera on the EUSO-Balloon gondola.
C-level mission requirements
In order to fullfill the C-level mission requirements sketched out in SRC1, the following mission
requirements arise :
[MRC1] Long duration flight operation (≥ 50 hours at night, TBC) of the EUSO-Balloon instrument in
trigger mode and in low background configuration. Altitude loss down to 35 (TBC) km is acceptable after
3 day/night transitions.
[MRC2] Measure temperature/altitude of cloud cover with the Infrared Camera
[MRC3] Fly a co-aligned laser on the gondola; generate laser induced events during taged data
acquisition.
[MRC4] Choose launch date to allow for a part of the flight over a high reflectivity surface (clouds, snow
...)
8 Mission Planning (TBD)
In this section, we present a possible mission planning for the EUSO-BALLOON payload. In order to fulfil
the requirements on all three levels, flight data has to be recorded under a variety of conditions.
This requires more that one balloon flight.
For the level A&B requirements - i.e first flight(s) - flight altitude and duration (during night-time) are
essential, for level C ("science" flight) requirement for mission planning is to access a large variety of
surface types.
To perform a complete end-to-end test of the JEM-EUSO qualification model and measure the
background in realistic flight conditions, the overflown parts of the globe should allow the observation of
a largest variety of conditions (uninhabited/sparsely habited; land/water; clouds/clear sky;
summer/winter, moonlit/moonless night, high latitude, one at low latitude). Note however that the
observation above an ocean is already in the B set of requirements – see [SRB1] above.
8.1 Number and date of required balloon flights
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[SRD] In order to produce useful input for the planning and construction of the JEM-EUSO mission, a first
flight (aimed at fulfilling at least the level A and a part of the B requirements) should take place no later
than summer 2013.
[SRE] In order to adjust trigger criteria and complete the B set of requirements, on or several further
flights are needed. The time interval between flights should be at least 3 months.
Successive (level C) flights are not as crucial for JEM-EUSO. These "science" flights can take place in 2014
and later, they present an important goal in their own right - beyond JEM-EUSO. Although the level B and
C requirements may be satisfied in one only long duration balloon flight we expect that three flights are
needed.
9 Operational requirements
With an estimated raw data rate of EUSO-BALLON of ~ 7.7 Gbits/sec – and still 18 Mbits/sec in the onboard selected event data – we estimate that 640 Gbit data has to recorded on-board on redundant
hard-disks - i.e. 64 Gbit per hour of flight. (estimate based on 324 kbyte/event)
[SRF] In order to ensure the realization of the objectives sketched out in sect 3 (mission objectives) even
in case of problems with recovering the payload, it is necessary to transfer a "contingency sample" of the
data to the ground during flight. A downlink rate of at least 1.3 Mbits/sec will ensure that a set of
triggered events at 0.5 Hz can be transferred to the ground in real time.
[MRF] downlink rate : 1.3 Mbits/sec (TBC - SIREN / NOSYCA compatible)
[SRG] The telecommands to be sent through NOSYCA to the payload include adjustment and tuning of
trigger-levels, as well as the command of a number subsystems.
[MRG] uplink rate : < 50 kb/s (TBC - SIREN / NOSYCA compatible)