Mission analysis work provides for off the Pioneer spacecraft probe flight schematics to Uranus, Saturn and Jupiter

Swenson, B. L.

English

NASA Technical Reports Server

• 4"¸ i
OUTER PLANET MISSION ANALYSIS OVERVIEW
MR. SWENSON: I think we have seen enough of programmatic
strategy but before we go into a description of the missions,
there are a few things we have to understand, particularly with
regard to flying probe missions off the Pioneer spacecraft.
Pioneer is an earth-line stabilized spacecraft, and this
presents some unique problems. The schematic for the deflection
is shown on the right-hand side of Figure 3-1. At some distance
as we approach the planet, we separate the probe, which is spin-
ning in the earth-line direction. After probe separation we
deflect the bus in order to miss the planet. The whole idea
behind the deflection maneuver is to deflect the bus in such a way
as to place it appropriately behind the probe so that the communi-
cation angle, the bus aspect angle, is in the aft hemisphere of
the spacecraft and, at the same time, the probe aspect angle,
after the probe enters and is descending vertically in the atmos-
phere, is very small.
However, with the Pioneer, we have the constraints that no
orientations off the earth line will be permitted, but we will
allow perpendicular and/or earth line maneuver capability. We
are assuming a very simple probe without any attitude control
systems and, therefore, orientations off the earth line are not
permitted.
Now with those constraints in mind, the Uranus mission
appears as shown in Figure 3-2.
This is a Uranus probe mission flown on a 1980 JU trajec-
tory which is really no longer in consideration programmatically,
but it is representative of the type of planetary approach. We
approach from nearly right onto the North pole. With the Pioneer
spacecraft, we try to swing by on the retrograde side. A Mari-
ner 79 JU would flyby on the posigrade side.
III-2
https://ntrs.nasa.gov/search.jsp?R=19750012295 2020-03-19T20:51:24+00:00Z
_.. "+¢. ;
E_.¸,_-!
._- ++-
i
<
W
"1-
0
Z
©
t-
(.2
uJ
.M
LL
UJ
Z
r,"
Z
0
Z
0
i
I--
LLI
._1
U.
I--
uJ w
0,..j
<_Z
tt " ]J I_\- <
wZ
m_
0
Z z
- 0 z
OW c¢
w _ w
Zw
w _Z w
0 _ _ w
w _ 0 0
mO_ Z_ Z_
=  "gZZ_Z wwu O--
ORIG_AL PAGE
oF poot_ qu_
III-3
,--4
I
"J
t_
_:i,..!_i._,.i_
ILl
ca
0
n,- D
C'1
Z .-
<
0z
Z
<
n-
n-
O
I--
D
o
w
"T" U2
I- _n
\ _ o
...t _-
/j" _rf"
_'-Z
m.. ol. -
ILl i_
o
09
0
tq
g
I'M
I
O7
o
D
b-'
-,.-t
r..
III-4
oRIGINAL pAGE _
OF pOO_% QUAL:'"_f
The reason the Pioneer flyby is on the retrograde side is to
provide a nearly zero angle of attack at entry. The probe hits
the atmosphere and descends and is turned by the rotation of the
planet during this time. During this descent period, we try to
maintain appropriate communication angles.
The spacecraft is pointing toward the Earth, and as shown,
the spacecraft Is nearly overhead of the probe through the entire
descent. _z)
The Saturn miSsion, shown on Figure 3-3, is for a 1981 dedi-
cated mission. Some thirty days prior to encounter with the planet,
we separate the probe. We deflect the spacecraft with a AV of
about 75 meters per second; when the probe enters, the spacecraft
is at the location shown on the figure at the time of entry. (Please
excuse the artistic license on the figure, the spacecraft isn't
quite that far around at the end of the probe mission.)
Again, the communication angles are fairly common, and the
spacecraft is directly overhead of the probe during the entire
descent.
The Titan mission is a little bit different. Over on the
left-hand side of the Figure 3-4 you see Saturn and Titan's orbit
at about 20 Saturn radii. The type of intercept that is attrac-
tive is an incoming intercept.
Some thirty days prior to encounter with Titan, we separate
the probe. After spacecraft deflection, the probe and the space-
craft travel nearly parallel trajectories.
Over on the right hand side of the figure you see a blowup of
the area of Titan.
At entry, we position the spacecraf£ so that we are about a
hundred thousand kilometers away. And, then, you can see that at
four hours after the entry we are occulted by Titan and we get a
RF occultation experiment at the same time.
III-5
Z _-O _
_ b-
O.
o _-_
I
0
","t
.> :" •i
ORIGINAL pAGE IS
OF POOR QUA_
. 111-6
- !7 "','
W
0
Z'-
<
I--
k.-
>.
.e"
wO
_l,--
O_
_N
k-
%
oKIG_qAL PAGE iS
OF POOR QUALITY
111-7
rThe Jupiter probe is shown on Figure 3-5. We have heard a
lot about the ephemeris improvement due to Pioneer I0. What it
means to us is that the one sigma ephemeris error is now approxi-
mately 468 kilometers. What this means, translated into a three
sigma entry angle error is that we can now expect to enter very
shallow with very small errors. In fact, for entry angles around
seven or seven and a half degrees, the three sigma entry angle
error i_ less than half a degree. That means we can be assured
withinthree sigma that we will enter no steeper than eight and
no shallower than about seven. This means that the heating is
I
greatly reduced, the accelerations are likewise greatly reduced,
and if the atmosphere is as friendly as we now think, we will be
able to get in with a lot of less heating.
The conclusions to all the mission analysis work can be put
into three main categories as shown on Figure 3-6. We have plen-
ty of launch capability for the Saturn and the Jupiter-Uranus
trajectories that we have looked at for Pioneer. We have 480
kilograms with a ten-day launch window off of a Titan Centaur 
TE 364.
In the Jupiter case, we have capability up to about eleven
hundred kilograms.
In all cases, the probe separation occurs about 30 days out,
with the exception of Jupiter where we separate about 50 days out.
And in all cases, the _V to deflect the spacecraft is less than
eighty meters per second.
The entry angle of attack for the probe is always low, less
than twenty degrees.'
In the communications area, the range is always less than a
hundred thousand kilometers. The probe.aspect angles can be made
to be very low and the spacecraft aspect angles are common to all
o
III-8
' !i ?]._7,
?"
7
t.lJ
I-
¢o
1.1..1
tl.l
0
,, / _z
tlJ
W
a. lnOdtMS
CD
,..o.
_ap 'HO_IH3 _T¢ONV AHIN3 ' _
Z>"
_-z
/_ ,LZZ
_o
• _ -_
ORIGINAL PAGE IS
OF POOR QUALITY
I
0
z
©
--I
z
_. o
° _ _ _
_ _ _,_,_ '_,,,
LI.I _.. f,.O
<
Q @
tD
I
0
.,-4
o__ o_:
OF _'_'_:_
III-i0
Yof the missions we have considered. That is, they all lie in
the aft hemisphere of the spacecraft.
With that as a backdrop of a description of the missions,
the next speaker, Lou Friedman, of JPL, will discuss taking these
missions and determining what the guidance and navigation require-
ments are for the probe mission.
III-ll


Outer planet mission analysis overview

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server