ElvisMartinS - 2002.12739.pdf

The

Case

for

Probe

class

NASA

Astrophysics

Missions

Lead Author:

Martin

Elvis

;

melvis@cfa.harvard.edu

;

phone

617

495

7442

Thematic

Activity

Space

Based

Activity

Authors

Jon

Arenberg

(Northrop Grumman)

jon.arenberg@ngc.com

David

Ballantyne

(Georgia

)

david.ballantyne@physics.gatech.edu

Mark

Bautz

(MIT)

mwb@space.mit.edu

Charles

Beichman

(JPL)

chas@ipac.caltech.edu

Jeffrey

Booth

(JPL)

jeffrey.t.booth@jpl.nasa.gov

James

Buckley

(Washington U., St.

Louis)

buckley@physics.wustl.edu

Jack

Burns

(

U.Colorado

, Boulder)

Jack.Burns@colorado.edu

Jordan

Camp

(NASA GSFC)

jordan.b.camp@nasa.gov

Alberto

Conti

(Ball Aerospace)

aconti@ball.com

Asantha

Cooray

(UC Irvine)

acooray@uci.edu

William

Danchi

(NASA GSFC)

william.c.danchi@nasa.gov

Jacques

Delabrouille

(CNRS

/APC Paris,

CEA

Saclay

)

delabrou@apc.in2p3.fr

Gianfranco De

Zotti

(INAF)

gianfranco.dezotti@inaf.it

Raphael

Flauger

(UC San Diego)

flauger@physics.ucsd.edu

Jason

Glenn

(

U.Colorado

, Boulder

)

jason.glenn@colorado.edu

Jonathan

Grindlay

(Harvard/

CfA

)

jgrindlay@cfa.harvard.edu

Shaul

Hanany

(U. MN)

hanany@umn.edu

Dieter

Hartmann

(Clemson)

hdieter@g.clemson.edu

George

Helou

(IPAC)

gxh@ipac.caltech.edu

Diego

Herranz

(

CSIC

UC, Santander)

herranz@ifca.unican.es

Johannes

Hubmayr

(NIST)

johanneshubmayr@gmail.com

Bradley

Johnson

(Columbia)

bradley.johnson@columbia.edu

William

Jones

(Princeton)

wcjones@princeton.edu

N. Jeremy

Kasdin

(Princeton)

jkasdin@princeton.edu

Chryssa Kouvoliotou

(G.Washington U.)

ckouveliotou@email.gwu.

Kerstin E.

Kunze

(U.

Salamanca)

kkunze@usal.es

Charles

Lawrence

(JPL)

charles.lawrence@jpl.nasa.gov

Joseph

Lazio

(JPL)

joseph.lazio@jpl.nasa.gov

Sarah

scy

(Ball Aerospace)

slipscy@ball.com

Charles

Lillie

(Lillie Consulting LLC)

<charles.lillie@clillie.com>

Tom

Maccarone

(Texas Tech U.)

Thomas.Maccarone@ttu.edu

Kristin

Madsen

(Caltech)

kkm@caltech.edu

Richard

Mushotzky

(U. MD)

richard@astro.umd.edu

Angela

Olinto

(U. Chicago)

aolinto@uchicago.edu

Peter

Plavchan

(George Mason U.)

pplavcha@gmu.edu

Levon

Pogosian

(Simon Fraser U.)

levon@sfu.ca

Andrew

Ptak

(NASA GSFC)

andrew.ptak@nasa.gov

Paul

Ray

(NRL)

paul.ray@nrl.navy.mil

Graca

M. Rocha

(JPL)

graca.m.rocha@jpl.nasa.gov

Paul Scowen

(

Arizona State U.

)

paul.scowen@asu.

Sara

Seager

(MIT)

seager@mit.edu

Massimo

Tinto

(JPL)

massimo.tinto@jpl.nasa.gov

John

Tomsick

(UC Berkeley)

jtomsick@

berkeley.edu

Gregory

Tucker

(Brown)

Gregory_Tucke

r@brown.edu

Mel

Ulmer

(Northwestern)

ulmer2@northwestern.edu

Yun

Wang

(Caltech/JPL)

wang@ipac.caltech.edu

Edward J.

Wollack

(

NASA/

GSFC)

edward.j.wollack@nasa.gov

THE

CASE

FOR

PROBE

CLASS

NASA

ASTROPHYSICS

MISSIONS

EXECUTIVE SUMMARY

Astrophysics spans an enormous range of questions on scales from individual planets to the

entire cosmos. To address the richness of 21

century astrophysics requires a corresponding

richness of telescopes spanning all bands and all messengers

Much scientific benefit comes

from having the multi

wavelength capability available at the same time

Most of the

bands

or measurement sensitivi

ties,

require space

based missions. Historically

NASA has addressed

this need

for breadth

with a small number of

flagship

class

missions and a larger number of

Explorer missions. While the Explorer program continues to flourish,

there is a

large

gap

between Explorers and

strategic missions

A fortunate combination of new astrophysics technologies with new

high capacity, low $/kg to

orbit

launchers

and new satellite buses allow for cheaper missions with capabilities

approaching

strategic missio

levels. NASA has recognized these developments by calling for

“Probe

class” mission ideas

for mission studies

Twenty

seven

proposals were received and 10

were funded

. The submissions spanned most of the

electromagnetic

spectrum from GeV

gamma

rays to th

far infrared,

and the new messengers of neutrinos and

ultra

high energy

cosmic rays

The key insight from the Probes exercise is that order

magnitude advances in

science performance metrics are possible across the board for initial

total

cost estimate

s in the

range $0.5B

$1B.

We advocate that the Astro2020 Decadal recommend a new line item for Probes be instituted

in the NASA Astrophysics Division budget

within the wedge for

large

new missions.

This

recommendation

would be in line with

the #2 priori

ty of the 2010 Decadal

in favor of

a vigorous

Explorer program.

This

new Probe

class mission

line would set a

mission

cost cap, as

the

succe

sful NASA Planetary Division’s New Frontiers

and Discovery

program

The Probes line

needs to be a significant

fraction of the budget over the de

cade covered by Astro

2020. Probes

will have costs in the range from just above the

MIDEX

Explorer cap ($2

without

a ~$50M

launch vehicle

) up to $1B

(total)

, the nominal lower bound for a

strategic

mission.

A cadence of

–

3 probes

per

decade

would be desirable

, and possible to integrate with a moderate flagship

funding line as well

Like the Explorer

line t

he Probes line would

need

protect

ion

against being

raided to pay for cost overruns in flagship missions

There are multiple

possible ways to

implement a Probes line to reap th

e maximum advantage for science

, but a key

recommendation is that

a “line” of Probes

enables

multi

mission development over this

decade, and into the future, wit

h flexibility to address new and broad astrophysics topics

KEY

SCIENCE GOALS AND

OBJECTIVES

The

readth of 21

Century astrophysics is staggering. The field is now truly multi

wavelength

and multi

messenger. The recent detections of neutrinos from a blazar and gravitational waves

from

both

merging black holes and neutron stars are only the latest surprises that th

e universe

has given up to our increasingly sophisticated instrumentation.

This richness is too great to be confined to a few questions. The full story of how the universe

began in a Big Bang and led to stars, galaxies, black holes, planets and, eventuall

y, life is

becoming clearer, but with huge unknowns. The nature of the Dark Sector (matter and energy),

the origin of seed black holes, the seemingly stubborn barriers to planet formation, and the

conditions needed for life to begin are all mysteries.

No s

ingle telescope can address this breadth in full.

Multiple

missions

over a range of sizes

are

needed to achieve balance in the program between fields, in order to maintain astronomy as

the vigorous science it has been for the past several decades.

suite

of telescopes is needed.

As per the

2017 National Academies report

“Powering Science:

NASA’s Large Strategic Science Missions”, flagships have a critical role to play. But given the

breadth of scientific return across wavelengths and scientific areas,

mult

iple missions are

required, and they cannot all be flagships nor take decades to develop.

For a long time the only formal channel for proposing smaller missions has been the Explorer

Program. This program is healthy, with ~4 missions/decade. While growth

there would be well

justified given the number of selectable proposals, the Explorer program only supports missions

up to $1

M (SMEX) or $250 M (MIDEX)

without launch vehicles

The budgets, and launch

capabilities (often only

to low Earth

orbit),

fill only a specific niche

in the

astrophysical discovery

space.

The question is whether missions smaller than flagships and larger than Explorers could achieve

the ambitious science goals that astronomers seek.

Certainly

would be strange

mportant

science can be done for less than $300 M, and important science can be done for more than $1

B, but that

the range $300 M

–

is a

gap.

Instead, a

s shown by the strong response to the

NASA probe call and the quality of the proposals

answer is a clear YES!

Probe

class missions

can be both ambitious and are affordable within a broad

based program

that provides flexibility

for the community

These probes will be making an order

magnitude or more gain over their

predecessor

’

measurements

–

or completely new measurements not possible at smaller scales

like Explorers

A series of probes may

yield more great science

than a Flagship of the same total cost as:

“

more bang for the buck

”:

a large observatory with

multiple

instruments (

e.g.

Hubble)

get

less time per instrument

and each instrument costs more per performance capability due to

the enhanced

integration and testing

needed

;

2. lowered risk:

one fails

still have the others;

better

launch schedule

the first

is ready much sooner

and

quite plausibly the whole

program

with

in the same time frame as the large

Flagship

mission

;

lower cost

: due to the

smaller launch vehicle, and class B

requirements

rather than

class

better o

ptimization

the

telescopes can be optimized for the task rather than being driven by

the most severe requirements

TECHNICAL OVERVIEW:

PROBE

CLASS MISSIONS

NASA Astrophysics has flown previous

robe

class (

i.e.

~$1 B) missions, as Paul Hertz has

pointed out

COBE, RXTE, Fermi, Kepler (

originally selected as a Planetary Division

Discovery

mission

and

Spitzer

. All of them were highly productive.

Spitzer was one of the “Great

Observatories”.

But has the potential of this mission class been exhausted?

To give a

more specific

answer

the

question

NASA Astrophysics

called for proposals to study “Probe

class” missions in the $0.5

–

$1 B

(including launch and Phase E)

range.

Twenty

seven

proposals were submi

NASA

and 1

were

select

for more detailed

study

The reports from these studies are all

now available

Several other studies have been funded by NASA

that are also in the “probe

class”

, such as the Solar

System Exploration Research Virtual Institute (SSERVI) study of a lunar

farside

radio array for astrophysics

, and two exoplanet studies previously done (E

C and Exo

S) looking at dedicated $1B

class exoplanet direct imaging missions.

Table

Comp

eted

Probe

Studies

Probe Study

Band

Closest Predecessor

AXIS

ray

Chandra

CDIM

Near

mid

SPHEREx, JWST

CETUS

GALEX,

HST

Earthfinder

Near

Ground

based radial velocity

GEP

Mid

IR,

Far

Herschel

, Spitzer

PICO

CMB

Planck

POEMMA

Cosmic rays

, neutrinos

Auger

Starshade

Optical

/NIR

WFI

RST

STROBE

ray

RXTE,

NICER

TAP

ray, IR, gamma

Swift

Farside

Radio

LWA,

MWA

, LOFAR

, SunRISE

Exo

Optical

/NIR

WFIRST

Exo

Optical/NIR

WFIRST

Farside

was funded separately from the other 10 probes through a SSERVI award, but is in family with

the main probe set.

The

PI is Jack Burns

(

U.Colorado

)

These were Probe studies done by

ExEP

2 years ago

–

the

Exo

C PI is Karl

Stapelfeldt

and the

Exo

S PI is

Sara

Seager

(MIT) (EXO

S evolved into the

Starshade

Rendezvous Probe).

Presentation at “The Space Astrophysics Landscape in the 2020s, slide 19, URL:

https://www.hou.usra.edu/meetings/landscape2019/presentations/Hertz.pdf

URL:

https://pcos.gsfc.nasa.gov/physpag/probe/probewp.php

and

https://cor.gsfc.nasa.gov/copag/probe

study.php

URL:

https://science.nasa.gov/astrophysics/2020

decadal

survey

planning

https://exoplanets.nasa.gov/exep/studies/probe

scale

stdt/

The key insight from these Probe studies

is that order

magnitude advances in science

performance metrics are possible across the board for initial cost estimates in the range $0.5B

$1B. This is possible because of investments in new instrument technologies and leveraging

commercial satellite

buses allows for missions with capabilities approaching flagship mission

levels, but at a significantly lower cost.

The advent of new, high

capacity, low $/kg

orbit

launchers from SpaceX, ULA, and Blue Origin, will continue to bring down the cost of th

ese

capable missions by encouraging rideshare opportunities for multiple assets on a single launch,

or affording the flexibility to optimize design and cost with more relaxed launch mass and

fairing constraints.

The

probe

class mission

studies

are credible

examples that

demonstrate the wide variety of

possible Probe

class missions

, but by no means exhaust the possibilities for scientif

ic discovery

at an affordable price point, while achieving programmatic balance

. The Probe studies showed

significant

scientific resilience as well, allowing the scope and design to be optimized for a given

cost target or launch constraint.

There is a

percepti

in parts of the community

that Probe science is necessarily highly

targeted whereas flagships have broad scien

While

lmost all

the

studied

Probes

derive their

parameters from a small number of key science objectives,

the

resulting

science impacts many

areas of astrophysics

in virtually every case

, and serve

a broad community of astrophysicists.

SUMMARY OF

COMPLETED PROBE STUDIES

ADVANCED X

RAY IMAGING SATELLITE (AXIS) is a major

mprovement over

Chandra

—

with

higher

resolution imaging over a larger field of view at much higher sensitivity, and

agile

operations allowing

Swift

like transient science.

Science include

: growth and fueling of

supermassive black holes

; g

alaxy formation and evolution

;

microphysics of cosmic plasmas

COSMIC DAWN INTENSITY MAPPER (CDIM)

will transform our understanding of the era of

reionization when the first stars and g

alaxies

formed

, and UV photons ionized the neutral

medium. CDIM

uses

wide area spectro

imaging surveys

provid

redshifts of galaxies and

quasars during reionization

and

crucial information on physical properties.

COSMIC EVOLUTION THROUGH UV

SPECTROSCOPY (CETUS) is a 1.5

m wide

field UV telescope

that will be a worthy successor to Hubble

With its wide

field camera, multi

object

spectrograph, and high

resolution echelle spectrograph, CETUS will maintain observational

access to the ultraviolet

(UV) after Hubble

and

also provide new and improved capabilities

EARTHFINDER

will perform high

precision

(cm/s)

radial

velocity (

PRV

)

measurements

tak

ing

advantage of:

broad wavelength coverage from the UV to NIR;

extremely compact, highly stable

and

efficient spectrometers

;

laser

based wavelength standards

;

high cadence observing

minimize sampling

nduced aliases;

and

absolute flux stability for

line

line analysis.

Taken from the probe study reports directly (Executive summary or Introduction).

GALAXY EVOLUTION PROBE (GEP)

will use the mid and far

IR to map the history of

galaxy

growth by star formation and accretion by super

assive black holes and their inter

relation,

and will measure the evolution of the interstellar medium and build

up of life

enabling

elements

over cosmic time.

PROBE OF INFLATION AND COSMIC ORIGINS (PICO)

is an imaging polarimeter that will scan the

sky for 5 years in 21

frequency bands spread between 21 and 799 GHz

It will produce full

sky

surveys of intensity and polarization with a

final combined

map noise le

vel equivalent to 3300

Planck missions for

the baseline required specifications, perform

ing

as 6400 Planck missions

PROBE OF EXTREME MULTI

MESSENGER ASTROPHYSICS (POEMMA)

observe

the Earth’s

atmosphere to

see

extensive air showers

from

cosmic rays

20 Ee

V and cosmic neutrinos

PeV

study

the origin of the highest

energy particles

;

neutrino emission

extreme transients

;

particle interactions at extreme energies;

uminous

ransient

vents

;

and

xotic particles.

STARSHADE RENDEZVOUS PROBE

operated in formation with the WFIRST observatory can

perform space

based direct imaging capable of discovering and characterizing exoplanets

around our nearest neighbor star systems. This first

its

kind combined mission will enable a

deep

dive exoplane

t investigation around these neighbor star systems

SPECTROSCOPIC TIME

RESOLVING OBSERVATORY FOR BROADBAND ENERGY X

RAYS (STROBE

X) combin

huge collecting area, broad energy coverage,

high

spectral

temporal resolution

agilit

y to

measur

mass and spi

map accretion

for

all

black hole mass

;

ap the

neutron

star

mass

radius relation

;

dentify

study X

ray counterparts

multiwavelength

multi

messenger transients

TRANSIENT ASTROPHYSICS PROBE (TAP

)

will characteriz

electromagnetic counterparts to

Gravitational Waves

for

mass scales from neutron stars to 10

⊙

Supermassive Black Hole

Binaries

and

many

time

domain astrophysical phenomena.

TAP is

n agile

multi

instrument

platform

with

ide

field X

ray

detectors

4π

gamma

ray monitors

, as well as

ray

and

wide

field

telescope

FARSIDE

leverages the Lunar Gateway

infrastructure to enable a

low frequency 128

node radio

array, completely deployed robotically, for studies of

magnetic fields in known exoplanet

ary

systems

EXO

would

use a de

dicated 1.4 m telescope and coronograph to

pectrally characterize at

least a dozen RV planets

earch >100 nearby stars at mul

ple epochs for planets down to

∼

3×10

contrast

, c

haracterize mini

Neptunes, search the

Centauri system

, and i

mage

hundreds of circumstellar disks

EXO

would use a dedicated

1.1 m telescope and 30 m starshade

for direct imaging and

spectral characterization

of giant planets down to Earth

size,

and

study complete

planetary

system as well

as circumstellar dust.

The Starshade

Rendezvous Probe concept

originally came

from this study

and was studied in more detail as per above.

There were about two dozen Probe

mission white papers submitted that were not selected.

While some of them may well not have been selectable, and some were duplicative, a number

clearly were selectable and were not chosen for want of program funding. Table 2 lists the

missions

from

the Cosmic Origins and PCOS web sites (see URLs above). The variety of

mission concepts indicates that there is great potential depth to the Probe

class mission class.

Table

A selection of

Probe White Papers

submitted to the NASA call fo

r concept

studies,

(based on public web sites

)

demonstrate

the great interest and broad diversity of

science possible in this intermediate mission

class

Mission

Band

Death of Massive Stars (DoMaS)

Gamma, X

ray, IR

Pete Roming

Inflation Probe

mm, sub

Ed Wollack

ray Grating Spectroscopy Probe

ray

Randall McEntaffer

HEX

Hard X

ray

Fiona Harrison

mHz Gravitational waves

Massimo Tinto

99 Luftballons

Near

Tim Eifler

Advanced Particle Telescope

Cosmic

rays

James Buckley

Time

domain Spectroscopic Observatory

rays, IR, gamma

Josh Grindlay

Wide

field X

ray Probe

rays

Andy Ptak

AMEGO

MeV, GeV

Julie McEnery

Probe

class Gravitational Wave Observatory

Sean McWilliams

GreatOWL

Cosmic rays

John

Mitchell

Probe

class Far

Far

C. Bradford

Dark Ages and Cosmic Dawn

Low

radio

Joe Lazio

WFXIS

ray

Mel Ulmer

ALLEGRO

ray

Mel Ulmer

ForEST

Optical/near

Howard MacEwen

HORUS

UV/optical

Paul Scowen

Deep Survey Telescope

Near

Fred Hearty

SHARP

Far

S. Rinehart

ORION

UV/optical

Paul Scowen

ATLAS

Near

, Mid

Yun Wang

Cosmic Origins & Destiny

Far

Christopher Walker

SUVO

UV/optical

Mel Ulmer

SPECTRAS

Mm, sub

Paul Goldsmith

A BALANCED PROGRAM FOR THE 2020

’

The

current

bifurcation of NASA Astrophysics missions between a very limited number of multi

billion dollar flagships and the roughly 10

50 times

cheaper Explorers

has

led to an unbalanced

program. There are alternatives. The NASA Planetary Division has t

he cost

capped

$1 B

New

Frontiers

and

$500 M

Discovery

program

, in addition to the

program’s flagship missions

The

New Frontiers missions to date

are Juno, New Horizons, and OSIRIS

Rex

, and there have been

many Discovery missions.

Cost caps do not typi

cally include the launch vehicle, or Phase E

operations

, but the astrophysics Probe studies did include these

(substantial)

items.

Given the

example program

atics from NASA’s Planetary Divis

ion, the

wealth of strong Probe

proposals

and the feasibility demonstrated by the selected studies there would seem to be no

technical obstacle to adopting a similar approach, with minor adjustments, for the Astrophysics

program.

Astrophysically, to maintain a broad

based program,

a cadence of 2

robe

class missions

per

decade would be both plausible and desirable. In order to encourage a range of Probe cost

levels, a division into

cost

sub

categories analogous to the

New Frontiers/Discovery

(or

MIDEX/SMEX)

division could be im

plemented.

ADVANTAGES

PROBES

hese medium

sized missions spread throughout the decade

has a

number of ad

antages that

will help to e

nsure U.S. leadership in astrophysical science

scientific

(responding to emerging science areas

science breadth through diversity,

opportunity for vast GO programs

)

;

participatory

(

multiple institutions and industries would be

engaged across a spectrum

of capabilities)

;

financial

(

smoothing

funding profiles across the decade through diversity of timelines

and peak spending years, lower cost missions have lower cost risk typically)

;

a deep bench

n increased

number of US scientists with experience in proposing for

and successfully managing large proposals. Increasing the 'bench' of investigators who

can PI scientific missions

will increase the diversity of scientific ideas for all mission

classes, resulting i

n a more innovative scientific program across the board

;

buying down

risk

. More ambitious, possibly flagship, versions will have

some of the

risk

retired

;

enable

technology development

Development

across

multiple

bands

continuously without hiatus.

IMPLEMENTATION

OPTIONS

There are multiple possible ways

that the Decadal might recommend

implement

ing

a Probes

line to reap the maximum advantage for science.

If t

he Astro2020 Decadal

Survey recommends

URL:

https://science.nasa.gov/solar

system/programs/new

frontiers

https://science.nasa.gov/solar

system/programs/new

frontiers

;

https://science.nasa.gov/solar

system/programs/discovery

the creation of a Probe line,

there is the

opportunity

to advise NASA on how to implement such

a program

as well.

Several options have been discussed:

1. Follow the

example

of the New Frontiers program

for

a new Astrophysics Probes program

with

competed, PI

led mission concepts that are constrain

ed to a subset of science priorities set

by the most recent Decadal Survey.

This allows the Decadal to guide a few areas of high priority

discovery space that could credibly be achieved in this price point

The Decadal Survey could, in theory,

recommend specific Probe missions for implementation

as part of a balanced

, strategic

program, avoiding a

direct competitive AO. NASA could

then

assign them to an implementing

NASA

center, and compete instruments

and/

or science teams.

Two caution

apply to

this approach: (a) Probes may

more likely to be

treated as Class A

missions,

leading to cost overrun issues; and (b) the science team will be less involved in

mission

details

, lead

ing

to poor

communications between the engineers and the scientists.

Emulate

the Explorer

and Discovery

program

for which

there are no restrictions (or

prioritization from the Decadal) on science, which allows the most flexibility. There could be

concerns about the potential burden on the

proposing community for

an open call on

such

large missions

, but it seems likely that the nature of ~$1B missions will limit credible proposers

to a manageable levels for community.

A concern

is that many proposals may be submitted at

considerable effort for each

A 2

phase subm

ission process might relieve some of the pressure.

No single approach need be chosen.

It may be that the Decadal concludes that a more guided

program is appropriate

for the near

term

, but that later Probe

missions

should be

unconstrained in order to be

abl

e to respond to the changing astrophysics landscape over the

latter part of the study.

A more detailed analysis of programmatic options for creating a Probe line is warranted in

order to maximize scientific return and insure programmatic balance.

TECHNOLOGY DRIVERS

Missions in the Probe

class, as evidenced by the completed study reports, do rely on advanced

technologies. Rather than

the current situation, where competed Explorers eschew

new

technology as much as possible, and large flag

hips take

all the technology cost risk, Probes

could allow a balanced approach to technology.

To provide probes with access to advanced technology, the SAT program (or

a related program

)

will need augmented funding.

Scaling

from

flagships, something like 3

5% of the probe

lifecycle cost would

appropriate. At 2 probes per decade, this would require an additional

~$5M/year in Astrophysics SAT funding. This is not negli

ble,

but

not

impossible

E.g.

the

APRA

program

just received a $5M/year

increase to su

pport

cubesats

Advancing technology readiness across such a broad spectrum of concepts would be balanced

by direct NASA funding through something like the Strategic Astrophysics Technology (SAT)

program

. If science areas are

driven by Decadal priorities, it would enable more strategic

investing by NASA. But the nature of a competition would still

incentivize proposers to invest in

their own technologies and avoid very high

risk technologies

that could blow a missions cost

cap

. Encouraging technological breakthroughs where they make the most impact in a price

point that allows teams to actually manage advancement is a great opportunity for Probes.

ORGANIZATIONS, PARTNERSHIPS, AND CURRENT STATUS

As evidenced by the breadth

of university, government, and industrial partners in the multiple

probe studies completed and submitted to date, it is clear that a large, divers

e collection of

the

community would benefit

from a series of Probe missions.

In addition

, while secondary to

scientific strength,

robust community participation in the

mission

science is desirable,

either through a GO

observing

program

where appropr

through

a significant early archival research program

ost Probes are amenable to

one or both

forms of

such a

program (

either

observationally, like

Spitzer

archival

ly,

Fermi

, or with data

product releases, like Gaia

)

. Existing data centers like STScI

, the CXC,

and IPAC could

disseminate Probe data the community broadly, as per NASA guidelines.

Funding

to support

probe science by GOs would be needed.

OST AND SCHEDULE

he wedge anticipated for large new miss

ion development

ultimately

~$7 B

over a decade.

Initial startup may be delayed in the 2020s due to already selected missions.

The ten Probe

studies included within their total cost cap of $1B both

launch and

Phase E operations.

Hence

the suggested

cadence of 2

3 Probe

cla

ss missions per decade

appears

plausible

$2B

$2.5B

This would require

a range of Probe cost levels

to average to ~$0.8B

to launch

division

of probes

into cost sub

categories analogous

to the New Frontiers/Discovery or

MIDEX/SMEX division could be implemented

to encourage a range of mission costs

A Probe

line on this scale would still allow the deve

lopment of a ~$5B Flagship mission in the same

decade, subject to funding peak compatibility.

The concurrency gained from having multiple powerful observatories operating together

is a

substantial gain o

ver having them sequentially. A

cadence of 3 Probes p

lus one Flagship per

decade going forward would, assuming extended missions, produce a revival or continuation of

the breadth of capability provided by the Great Observatories.

The Probe

class mission line would need to be protected against being raided to

pay for cost

overruns in flagship missions,

in a manner similar to

the Explorer program.

Probe

class

missions

spread throughout the decade would

smooth

funding profiles across the decade through

the

diversity of

their

melines and spending peaks. Also l

ower cost missions

often

have lower

risk

CONCLUSIONS

The

key

question for

Probes is

whether there is compelling science

in the

wide

cost

range

between

Explorer

and

lagship

. It seems self

evident

that there is no

scientific desert

between those extremes

. T

NASA

Probe studies

, summarized here

and submitted se

parately

provide clear examples

that yes, there is a rich diversity of

forefront

science

able

at the

Probe scale.

Some of the science

can

only

be done

efficiently

at that scale, driven by the

scientific requirements for discovery and u

nderstanding.

inally

these studies

demonstrate

that

for a given cost or technical targe

, t

he astrophysics community has the creativity to meet that

target

. Wh

atever

the

cost cap

the scientists and engineers in our community

will meet the

challenge for Probes and provide

a compelling, continuing program for astrophysical discovery.