# NanoSent19Nov04.doc ECR to SSSC Roadmap Committee 19 November 2004

# 

## **The NanoSentinels Concept**

**[Concept:]{.underline}**

Many (\~32) battery-powered /solar-cell-recharged nano-sentinels (5-10
kg) distributed around 360in the ecliptic r\~1AU to detect ICMEs
(interplanetary coronal mass ejections) and SEP (solar energetic
particle) events.

Mother ship will launch nano-sentinels into dispersal orbits using lunar
swing-by(s).

Nanosats should be launched into \~1AU orbits. Lunar swing-bys from
transfer orbit (to produce longitude lags and leads) will distribute
them around 360. We need a good orbital analysis to estimate required V.

These near-1AU orbits very effectively complement the LWS *[INNER
Heliospheric Sentinels (IHS]{.underline})*, that currently are a
scientific mission to understand the essential physics of solar events
(flares, CMEs, SEPs) well inside of 1AU. *[NanoSentinels]{.underline}*
will provide the measurements of the *actual* disturbances that cross
1AU.

**[Main science goal]{.underline}** is to understand how solar
disturbances propagate to \~1 AU.

This would be complementary to LWS and Exploration objectives.

> Engineering approach: Better to obtain data at radius of interest that
> to study the physical processes at other (inner) locations.

**[Exploration:]{.underline}** NanoSentinels would provide
greatly-improved engineering-level data on the radiation environment
near Earth-Mars orbits.

Main interest is in large solar events. Therefore nanosats should be
*fully deployed* by rise of solar cycle (2017)---certainly no later than
maximum (2019-2021) and last at least another \~4-6 years through the
large post-maximum events (to 2022-2016).

Solar events (flare particles, CMEs) have durations of 2-4 days
(\~50-100 hours).

Even if event triggers work perfectly, this gives coverage of \~10-20
events during the lifetime.

If NanoSentinels are deployed during Earth-Mars-Earth transit, would
give 0.4 AU warning (\~1-2 days) of ICME/energetic storm particle event.

During solar max, there are \~3-6 large events/year *at Earth*. There
are probably \~4 times more than this around the entire Sun, *i.e.,*
\~20/year.

False alarms (inevitable) must be minimized.

Event trigger algorithms are crucial. Don't want to waste power on false
alarms. *Genesis* CME algorithms worked well (but had full-time
plasma/field instrumentation and sophisticated information processing).

Could event triggers be communicated to (and activate) adjacent (all)
spacecraft, so as to get definitive longitude coverage?

### Mission Technology

DSN tracking requirements must be scrutinized. Feasibility increased by
augmented capability of DSN (\~200-400 arrays of 12 m dishes---Chuck
Holmes). There is no need for real-time data (unless this is sold as an
operational system). Weekly (or even monthly) downloads (targets of
opportunity) would be adequate.

Magnetometers are *essential* and preferably should be taking data *all
the time*. Scientific community believes that a great deal of the
*context* of ICME and SEP event structure and dynamics can be understood
from magnetic field behavior.

Battery lifetime\~1000 h is marginal. Batteries must be re-charged by
\~1W solar cells.

If solar cells (\~1W) can re-charge battery between solar events, then
mission could have a lifetime of a solar cycle (consumables are
negligible)

[Deployment]{.underline} can then take place over \~7 years and still be
ready for rise of solar acitivity in 2017.

The part of the scientific community interested in relationship between
solar and heliospheric fields would be grateful to have NanoSentinels in
dispersal phases (\<180) during later phase of Solar Cycle 24 (*e.g.,*
2012-2017) when polar coronal holes extend to the equator.

### Spacecraft Systems:

Mass 5 kg

Structure 1 kg

S/C systems 1 kg

Batteries (Li) 2 kg

Instruments 1 kg

Solar cells 1W

Low-power instruments 50 mW

Battery lifetime 1000 h @ 1/4 W

Whip antenna

Passive (gravity gradient) orientation

Attitude knowledge 1 or 2 solar sensors (phase is a problem)

Roll rate \~minutes

Chips 1 mW/channel

Processor 15 mW

**[Operating mode]{.underline}:**

Usually operate in power-down mode (W)

Awakened by trigger (flare?) to take data for small periods of time
(\~50-100 hrs) during events

**[Instrument Payload and Requirements:]{.underline}**

[Instrument scientific priorities:]{.underline}

1.  Magnetometer

2.  Faraday cup

3.  Energetic particle spectrometer

4.  Xray spectrometer

Magnetic field

Dynamic range 0.1-100 nT

Time resolution\~0.1-1 s

> Could get away with just field magnitude \|**B**\| for phenomenology,
> but plasma structures and especially energetic particles require
> direction

Plasma

Faraday cup

> Must capture peak of solar wind beam (\<10 half-angle) *and* have
> knowledge of cup normal direction (relative to radial).
>
> Cup could have half-angle opening of \~45.
>
> Requires square-wave high voltage to discriminate against
> photo-electron current.

Energetic particles

\>30 keV-5 MeV electrons and ions

Near-relativistic (30keV-1MeV electrons are a useful proxy for
\>20MeV/nuc ions)

> Two SSD detectors in anti-coincidence looking out 180 opposing
> collimators. If aligned with s/c axis, and s/c axis is approximately
> radial to sun, then this would give an effective fluence monitor.

Xray photometer

\>10 keV

Good for detecting backside flares

Natural for burst mode

Could act as event (flare) triggers

Probably not necessary on all S/C

#### Technical Notes

Possible dual primary Delta II (TIMED)

Gimballed antenna dish? Constraint on attitude control system

Phased array? Have knowledge of attitude.

Fan beam (1D). Still need one degree of knowledge.

Pancake antenna (in ecliptic)

Star sensor (Canopus/ S ecliptic pole). Always 90 deg from Sun.

Carrier from DSN.

Slow spin rate for stability

Relays limited by small dish size

100000 bits/CME takes 28 hours