# Presentation: 016105

## Sentinels Splinter

## Summary of Sentinels Issues

·	Is the current definition of the Sentinels the right one? Are 4 Inner Heliospheric Sentinels (IHS) plus 1 Far Side Sentinel the right choices?

		· Is the L1 Sentinel part of LWS?  

·	Is the current launch schedule right? Should Sentinels launch earlier?

·	Can we overlap with STEREO?

·	What are the optimum IHS and FSS orbits? 

·	What data needs to come down in real time?

·	Should we measure >100 MeV particles?

·	Should Sentinels monitor the Solar Irradiance?

·	How important are Far Side Helioseismology measurements?

·	What technologies need to be developed?

- ·	Is the current definition of the Sentinels the right one? Are 4 Inner Heliospheric Sentinels (IHS) plus 1 Far Side Sentinel the right choices?
- 		· Is the L1 Sentinel part of LWS?
- ·	Is the current launch schedule right? Should Sentinels launch earlier?
- ·	Can we overlap with STEREO?
- ·	What are the optimum IHS and FSS orbits?
- ·	What data needs to come down in real time?
- ·	Should we measure >100 MeV particles?
- ·	Should Sentinels monitor the Solar Irradiance?
- ·	How important are Far Side Helioseismology measurements?
- ·	What technologies need to be developed?

## Is the current definition of the Sentinels the right one? 

- Current definition:
- - 4 Inner Heliospheric Sentinels covering 0.5-.95 AU in ecliptic
- (Fields and particles, spinner, inclination < 10 degrees)
- - 1 Far Side Sentinel starting at 180 and later drifting to 220                     	       degrees
- (Fields and particles + helioseismology+ EUV, 3 axis stabilized)
- Should we have fewer Sentinels and try to get out of the ecliptic?
- - How important is the 3D structure of the heliosphere?
- - Should the Solar Polar Imager be launched earlier?
- - Should solar sail technology development be accelerated?
- - How will ESA's Solar Orbiter fit in with LWS?
- - How will Japan's L5 mission fit in with LWS?
- Do we need a coronagraph at 90 degrees to replace STEREO?

## Is Far Side Sentinel needed for the heliospheric goals ?

***Is it a "Solar" mission in disguise?***
- Need to monitor backside to relate *in situ* observations to solar activity
-        Unique measurements by FSS:
- · Monitor active regions, energetic particle sources on back side approaching the limb (EUV)
- ·Measure photospheric magnetic fields on backside
- 	Follows evolution of flux on backside
- 	Creates better boundary conditions for coronal magnetic field 		models
- How important is FSS helioseismology?
- Two spacecraft separated >90 degrees needed to see deep into convection zone to see flux rising for even longer forecasting times
- 		These measurements crucial to improve theoretical models of 			convection zone -- Current models break down; need 				constraints from observations

## Is the current LWS launch schedule right?

- LWS Goal: SDO, Sentinels, and Mappers in place for Solar Maximum in 2010
- Sentinels prefer rising phase while Mappers prefer declining phase
- Sentinels need 1 year to get on station
- Launching Sentinels before Mappers lowers cost of Mappers by reducing lifetime requirement.
- Sentinel lifetime less of an issue because of design, location
- Launching Sentinels before SDO gives good overlap with STEREO
-     STEREO launches in 2004 and drifts 22 degrees/year
- 4 years to ~90 degrees
- What is the optimum timing with respect to STEREO?

## Is the L1 Sentinel part of LWS? 

- Upstream solar wind monitor is required.
-            Who is supplying it?
- ·What is the definition of the L1 Sentinel?
- How many spacecraft at L1?
- Effect of spatial gradients in solar wind on magnetosphere not understood
- One option: 1 L1 spacecraft with magnetic field and solar wind plus several others at L1 with only magnetometers

## What are the optimum IHS and FSS orbits?

** **
- Many options for orbits of the 4 IHS spacecraft
- Optimize for coverage of Earth-Sun line?
- Optimize for radial alignment?
- Many options for Far Side orbit
- Start at 180 and drift?
- Start at 120 and drift backward?
- Use SEP so not limited by drift orbits?
- What is optimum location for helioseismology ?

## Sentinels Mission Design Issues

- What data needs to come down in real time?
- What data needs rapid (minutes) processing?
- Commerical vs. custom spacecraft bus?
*	**	**Need trade studies on orbits, data rates, etc.*

##  Sentinels Science Instrumentation Issues

- Should we measure high (>100 MeV) particles?
- Relevance to astronauts: Not required for actual monitoring, but are necessary to develop understanding of the acceleration process.
- These require larger, heavier instruments than in current Sentinels concept
- Should this be done outside of LWS? (STP, Explorer?)
- Should we measure solar irradiance from all Sentinels?