Since the Sun contains essentially all of the mass of the solar system, its composition defines average solar system composition. For many elements there are, however, significant differences between the composition of the Sun and various other parts of the solar system (planets, comets, meteorites, ...). These differences are very revealing as to the conditions that prevailed and the pro-cesses that occurred in the formation and evolution of the so-lar system. It is also true that the composition of the Sun is not well established for the purposes of planetary science. Compilations of solar abundances are based mainly on analyses of CI chondrite meteorites, rather than on direct measurements of the Sun. There are significant limitations to this approach and accurate direct measure-ments of solar abundances would be extremely important for planetary science.
Isotopic differences also exist among various planetary materials. Although these are much smaller, percentage-wise, than the elemental differences, they are of great importance because, in general, these would not occur with most of the chemical and physical processes that produce differences in elemental compositions. It is independently known that the solar system was formed from a wide variety of interstellar materials produced over the approximately 10 billion years of galactic history prior to the formation of the solar system and that these materials had a great diversity of isotopic compositions compared to those found on Earth. The isotopic compositions of solar matter define solar system averages and thus represent the starting point for the interpretations of the isotopic differences among planetary materials. A major specific application is assessing the processes by which planetary atmospheres formed using observed differences in isotopic compositions compared to solar. Essentially nothing is known about solar isotopic compositions. Providing these data is a major goal of the Genesis mission.
The Genesis mission will return samples of solar matter to Earth. It will lead to:
(1) a major improvement in our knowledge of the average chemical and isotopic composition of the solar system.
(2) a reservoir of solar material for 21st century science.
(3) greatly improved models of the nebular processes by which plan-etary materials and the various bodies in the solar system (planets, comets, asteroids, Kuiper belt, bodies yet to be discovered, etc.) formed.
From a consideration of which elements and isotopes are most im-portant, a set of prioritized Measurement Objectives has been developed (Table 1). The isotopic compositions of C, N, O, Noble gases and the elements listed in Measurement Objective 7 are high priority measurements because meteorite studies have revealed systematic isotopic differences among planetary materials for these elements. Except for 20Ne/22Ne, solar data are not available, and the solar and terrestrial 20Ne/22Ne ratios differ by 38%. Lunar data have been interpreted to indicate that the 15N/14N ratio in the solar wind has systematically increased over the age of the solar system. This crucial interpretation will be directly tested by the Genesis data. More discussion of these Objectives is available in the Science section of the Genesis Discovery 5 Step 1 proposal. Relevant proposal sections are cross-references in Table 1, but note that there are minor revisions between Table 1 and the equivalent proposal table E1-2.
Based on feasibility, some measurements have been scheduled for early analysis and publication within one year after sample return to assure the timeliness of reporting the results of the Genesis mission. These are designated as the Early Science Return on Table 1.
Table 1. Prioritized Measurement Objectives Proposal Sections
| (1) O isotopes. | Box 1-2 (foldout) |
| (2) N isotopes in bulk solar winda. | E1.C.2, E1.C.3 |
| (3) Noble gas elements and isotopesa. | E1.C.2 |
| (4) Noble gas elements and isotopes; regimes. | E1.D |
| (5) C isotopesa. | E1.D |
| (6) C isotopes in different solar wind regimes. | E1.D |
| (7) Mg,Ca,Ti,Cr,Ba isotopes. | E1.C.1, E1.C.4.b |
| (8) Key First Ionization Potential Elements. | E1.D |
| (9) Mass 80-100 and 120-140 elemental abundance patterns. | E1.C.4.b |
| (10) Survey of solar-terrestrial isotopic differences. | E1.C.1, E1.C.4.b |
| (11) Noble gas and N, elements and isotopes for higher energy solar particles. | E1.C.5.a |
| (12) Li/Be/B elemental and isotopic abundances. | E1.C.4.c, E1.C.5.b |
| (13) Radioactive nuclei in the solar winda. | E1.C.5.b |
| (14) F abundance. | E1.C.5.b |
| (15) Pt-group elemental abundances. | E1.C.1 |
| (16) Key s-process heavy elements. | E1.C.4.a |
| (17) Heavy-light element comparisons. | E1.C.4.c |
| (18) Solar rare earth elements abundance pattern. | E1.C.1 |
| (19) Comparison of solar and chondritic elemental abundances. | E1.C.1 |
Table 2 provides the requirements on precision and accuracy.
Table 2. Precision and Accuracy of Elemental and Isotopic Analyses
| Elemental Accuracy (2 sigma limits) =
±10% of the number of atoms of each element per cm2 on
the collector materials
Isotopic Precision (2 sigma limits on the relative number of the different isotopes of an element compared to a terrestrial reference standard)
(a) For the rare isotopes: 78Kr, 124Xe, 126Xe, 1% may not be achievable. A goal for these isotopes is better than ± 3%, 2 sigma. |
It is now well established that the solar wind is accelerated by more than one mecha-nism, leading to at least three major solar wind regimes: the high-speed wind from coronal holes, the low-speed interstream wind, and the transient wind associated with coro-nal mass ejections. Measurements by in-situ solar wind instruments have shown that there is a fractionation of matter between the photosphere and the solar wind which de-pends on the first ionization time (FIT) and, to a lesser extent, on the ion mass and charge. The Genesis mission will collect separate samples for each of the three regimes in order to correct the Genesis elemental abundance data for these fractionation effects. The solar wind monitor data from Genesis will be combined with knowledge of the systematics of FIT, mass, and charge fractionation patterns obtained from prior missions to model the corrections to be applied to the Genesis sample data to deduce the elemental composition of the photosphere.
It is not known whether solar wind isotopes are fractionated relative to the photosphere. Genesis data will test this by comparing isotopic compositions in the different solar wind regimes. If there are no differences, it is very likely that solar wind and photospheric isotopic compositions can be equated. If differences are observed, the systematics of the data can be used to model corrections.
The ability to measure the abundances of various solar wind atoms depends on collecting enough material to significantly exceed the background of impurity atoms. Expected solar wind fluences are given in Table 3. In the case of oxygen, collector material purity is too low to give adequate signal to noise in a two year exposure; consequently, an electrostatic concentrator is required to give enhanced fluences.
Table 3. Estimated Composition of Bulk Solar Wind (1)
|
Z |
Element |
Solar system abund
(Note 2) |
Solar wind flux
(cm-2s-1) |
2-yr. Fluence
(cm-2) |
ppma
(Note 3) |
ppmw
(Note 4) |
|
3 |
Li |
5.7E+01 |
1.7E+00 |
1.1E+08 |
2.2E-04 |
5.3E-05 |
|
4 |
Be |
7.3E-01 |
2.2E-02 |
1.4E+06 |
2.8E-06 |
8.9E-07 |
|
5 |
B |
2.1E+01 |
6.4E-01 |
4.0E+07 |
8.0E-05 |
3.1E-05 |
|
6 |
C |
1.0E+07 |
1.0E+05 |
6.3E+12 |
1.3E+01 |
5.4E+00 |
|
7 |
N |
3.1E+06 |
3.1E+04 |
2.0E+12 |
3.9E+00 |
2.0E+00 |
|
8 |
O |
2.4E+07 |
2.4E+05 |
1.5E+13 |
3.0E+01 |
1.7E+01 |
|
9 |
F |
8.4E+02 |
8.4E+00 |
5.3E+08 |
1.1E-03 |
7.2E-04 |
|
10 |
Ne |
3.4E+06 |
3.4E+04 |
2.2E+12 |
4.3E+00 |
3.1E+00 |
|
11 |
Na |
5.7E+04 |
1.7E+03 |
1.1E+11 |
2.2E-01 |
1.8E-01 |
|
12 |
Mg |
1.1E+06 |
3.2E+04 |
2.0E+12 |
4.1E+00 |
3.5E+00 |
|
13 |
Al |
8.5E+04 |
2.5E+03 |
1.6E+11 |
3.2E-01 |
3.1E-01 |
|
14 |
Si |
1.0E+06 |
3.0E+04 |
1.9E+12 |
3.8E+00 |
3.8E+00 |
|
15 |
P |
1.0E+04 |
2.1E+02 |
1.3E+10 |
2.6E-02 |
2.9E-02 |
|
16 |
S |
5.2E+05 |
1.0E+04 |
6.5E+11 |
1.3E+00 |
1.5E+00 |
|
17 |
Cl |
5.2E+03 |
5.3E+01 |
3.3E+09 |
6.7E-03 |
8.3E-03 |
|
18 |
Ar |
1.0E+05 |
1.0E+03 |
6.4E+10 |
1.3E-01 |
1.7E-01 |
|
19 |
K |
3.8E+03 |
1.1E+02 |
7.1E+09 |
1.4E-02 |
2.0E-02 |
|
20 |
Ca |
6.1E+04 |
1.8E+03 |
1.2E+11 |
2.3E-01 |
3.3E-01 |
|
21 |
Sc |
3.4E+01 |
1.0E+00 |
6.5E+07 |
1.3E-04 |
2.1E-04 |
|
22 |
Ti |
2.4E+03 |
7.2E+01 |
4.5E+09 |
9.1E-03 |
1.5E-02 |
|
23 |
V |
2.9E+02 |
8.8E+00 |
5.5E+08 |
1.1E-03 |
2.0E-03 |
|
24 |
Cr |
1.4E+04 |
4.0E+02 |
2.6E+10 |
5.1E-02 |
9.4E-02 |
|
25 |
Mn |
9.6E+03 |
2.9E+02 |
1.8E+10 |
3.6E-02 |
7.1E-02 |
|
26 |
Fe |
9.0E+05 |
2.7E+04 |
1.7E+12 |
3.4E+00 |
6.8E+00 |
|
27 |
Co |
2.2E+03 |
6.7E+01 |
4.3E+09 |
8.5E-03 |
1.8E-02 |
|
28 |
Ni |
4.9E+04 |
1.5E+03 |
9.3E+10 |
1.9E-01 |
3.9E-01 |
|
29 |
Cu |
5.2E+02 |
1.6E+01 |
9.9E+08 |
2.0E-03 |
4.5E-03 |
|
30 |
Zn |
1.3E+03 |
3.8E+01 |
2.4E+09 |
4.8E-03 |
1.1E-02 |
|
31 |
Ga |
3.8E+01 |
1.1E+00 |
7.2E+07 |
1.4E-04 |
3.5E-04 |
|
32 |
Ge |
1.2E+02 |
3.6E+00 |
2.3E+08 |
4.5E-04 |
1.2E-03 |
|
33 |
As |
6.6E+00 |
2.0E-01 |
1.2E+07 |
2.5E-05 |
6.6E-05 |
|
34 |
Se |
6.2E+01 |
1.9E+00 |
1.2E+08 |
2.4E-04 |
6.6E-04 |
|
35 |
Br |
1.2E+01 |
1.2E-01 |
7.3E+06 |
1.5E-05 |
4.2E-05 |
|
36 |
Kr |
4.5E+01 |
4.5E-01 |
2.8E+07 |
5.7E-05 |
1.7E-04 |
|
37 |
Rb |
7.1E+00 |
2.1E-01 |
1.3E+07 |
2.7E-05 |
8.2E-05 |
|
38 |
Sr |
2.3E+01 |
7.0E-01 |
4.4E+07 |
8.9E-05 |
2.8E-04 |
|
39 |
Y |
4.6E+00 |
1.4E-01 |
8.8E+06 |
1.8E-05 |
5.6E-05 |
|
40 |
Zr |
1.1E+01 |
3.4E-01 |
2.2E+07 |
4.3E-05 |
1.4E-04 |
|
41 |
Nb |
7.0E-01 |
2.1E-02 |
1.3E+06 |
2.6E-02 |
8.7E-06 |
|
42 |
Mo |
2.5E+00 |
7.6E-02 |
4.8E+06 |
9.7E-06 |
3.3E-05 |
|
44 |
Ru |
1.9E+00 |
5.6E-02 |
3.5E+06 |
7.0E-06 |
2.5E-05 |
|
45 |
Rh |
3.4E-01 |
1.0E-02 |
6.5E+05 |
1.3E-06 |
4.8E-06 |
|
46 |
Pd |
1.4E+00 |
4.2E-02 |
2.6E+06 |
5.3E-06 |
2.0E-05 |
|
47 |
Ag |
4.9E-01 |
1.5E-02 |
9.2E+05 |
1.8E-06 |
7.1E-06 |
|
48 |
Cd |
1.6E+00 |
4.8E-02 |
3.0E+06 |
6.1E-06 |
2.4E-05 |
|
49 |
In |
1.8E-01 |
5.5E-03 |
3.5E+05 |
7.0E-07 |
2.9E-06 |
|
50 |
Sn |
3.8E+00 |
1.1E-01 |
7.2E+06 |
1.4E-05 |
6.1E-05 |
|
51 |
Sb |
3.1E-01 |
9.3E-03 |
5.8E+5 |
1.2E-06 |
5.1E-06 |
|
52 |
Te |
4.8E+00 |
1.4E-01 |
9.1E+06 |
1.8E-05 |
8.3E-05 |
|
53 |
I |
9.0E-01 |
1.8E-02 |
1.1E+06 |
2.3E-06 |
1.0E-05 |
|
54 |
Xe |
4.7E+00 |
4.7E-02 |
3.0E+06 |
6.0E-06 |
2.8E-05 |
|
55 |
Cs |
3.7E-01 |
1.1E-02 |
6.9E+05 |
1.4E-06 |
6.7E-06 |
|
56 |
Ba |
4.5E+00 |
1.3E-01 |
8.5E+06 |
1.7E-05 |
8.3E-05 |
|
57 |
La |
4.5E-01 |
1.3E-02 |
8.4E+05 |
1.7E-06 |
8.3E-06 |
|
58 |
Ce |
1.1E+00 |
3.4E-02 |
2.2E+06 |
4.3E-06 |
2.1E-05 |
|
59 |
Pr |
1.7E-01 |
5.0E-03 |
3.2E+05 |
6.3E-07 |
3.2E-06 |
|
60 |
Nd |
8.3E-01 |
2.5E-02 |
1.6E+06 |
3.1E-06 |
1.6E-05 |
|
62 |
Sm |
2.6E-01 |
7.7E-03 |
4.9E+05 |
9.8E-07 |
5.2E-06 |
|
63 |
Eu |
9.7E-02 |
2.9E-03 |
1.8E+05 |
3.7E-07 |
2.0E-06 |
|
64 |
Gd |
3.3E-01 |
9.9E-03 |
6.2E+05 |
1.2E-06 |
7.0E-06 |
|
65 |
Tb |
6.0E-02 |
1.8E-03 |
1.1E+05 |
2.3E-07 |
1.3E-06 |
|
66 |
Dy |
3.9E-01 |
1.2E-02 |
7.5E+05 |
1.5E-06 |
8.6E-06 |
|
67 |
Ho |
8.9E-02 |
2.7E-03 |
1.7E+05 |
3.4E-07 |
2.0E-06 |
|
68 |
Er |
2.5E-01 |
7.5E-03 |
4.7E+05 |
9.5E-07 |
5.6E-06 |
|
69 |
Tm |
3.8E-02 |
1.1E-03 |
7.2E+04 |
1.4E-07 |
8.6E-07 |
|
70 |
Yb |
2.5E-01 |
7.4E-03 |
4.7E+05 |
9.4E-07 |
5.8E-06 |
|
71 |
Lu |
3.7E-02 |
1.1E-03 |
6.9E+04 |
1.4E-07 |
8.7E-07 |
|
72 |
Hf |
1.5E-01 |
4.6E-03 |
2.9E+05 |
5.8E-07 |
4.2E-06 |
|
74 |
W |
1.3E-01 |
4.0E-03 |
2.5E+05 |
5.0E-07 |
3.3E-06 |
|
75 |
Re |
5.2E-02 |
1.6E-03 |
9.8E+04 |
2.0E-07 |
1.3E-06 |
|
76 |
Os |
6.8E-01 |
2.0E-02 |
1.3E+06 |
2.6E-06 |
1.7E-05 |
|
77 |
Ir |
6.6E-01 |
2.0E-02 |
1.3E+06 |
2.5E-06 |
1.7E-05 |
|
78 |
Pt |
1.3E+00 |
4.0E-02 |
2.5E+06 |
5.1E-06 |
3.5E-05 |
|
79 |
Au |
1.9E-01 |
5.6E-03 |
3.5E+05 |
7.1E-07 |
5.0E-06 |
|
80 |
Hg |
3.4E-01 |
6.7E-03 |
4.3E+05 |
8.7E-07 |
6.1E-06 |
|
81 |
Tl |
1.8E-01 |
5.5E-03 |
3.5E+05 |
6.9E-07 |
5.1E-06 |
|
82 |
Pb |
3.2E+00 |
9.4E-02 |
6.0E+06 |
1.2E-05 |
8.8E-05 |
|
83 |
Bi |
1.4E-01 |
4.3E-03 |
2.7E+05 |
5.5E-07 |
4.0E-06 |
|
90 |
Th |
3.4E-02 |
1.0E-03 |
6.3E+04 |
1.3E-07 |
1.1E-06 |
|
92 |
U |
9.0E-03 |
2.7E-04 |
1.7E+04 |
3.4E-08 |
2.9E-07 |
| No. | Requirement | Rationale | Comments |
| 1-1 | Measure the elemental and isotopic abundances of solar wind ions to the accuracies or precisions given in Table 2. | This is the most important objective of the mission. | Priorities in Table 1. The concentrator is being developed to meet the precision requirements for O isotopes, the highest priority objective. |
| 1-2 | In addition to a bulk sample, collect separate samples for each of 3 solar-wind regimes: low speed, coronal hole, and coronal mass ejections. | To provide fundamental understanding of regime composition; to enable cor-rections for any differences between the compositions of the solar wind and the solar photosphere. | Requires monitor instruments to measure ion velocity, ion temperature, alpha:proton ratio, and electron distributions. A science algorithm will utilize the monitor data to set concentrator voltages and select collector arrays for specific regimes. |
| 1-3 | Provide a reservoir of solar matter for analysis in the 21st century. | This is a high priority objective of the mission. It avoids the necessity of a series of solar wind sample return missions. | This requirement primarily affects collector area (Req. 3.1-2 and 3.1-3). A Science Analysis goal is that no more than 50% of the returned collector array and target materials be used during Genesis sample analysis. This requirement generates a requirement to plan for long term curation. (Req. 3-5). |
| No. | Requirement | Rationale | Comments |
| 2-1 | Expose the collectors to the solar wind sunward of the Earth's bow shock. | Necessary to eliminate contamination of solar wind sample by terrestrial material and perturbations from the terrestrial magnetic field. | General requirement is firm. L1 halo orbit is adequate. |
| 2-2 | Collect the bulk sample of solar wind ions for a period of at least 22 months. | This exposure is required to meet concentrator fluence requirements. | There are no science requirements on the launch date. |
| 2-3 | Return collected samples to Earth for analysis. | Advanced analyses in Earth labs required to achieve required accuracies. | This is a firm requirement. Present Baseline mission is for mid-air recovery of collector materials in a Sample Return Capsule (SRC). |
| No. | Requirement | Rationale | Comments |
| 3.1-1 | Collector design shall be compatible with a variety of array materials. | Required to match different elements to analytical techniques. | Likely collector array materials are Si, diamond, Ge, and films deposited on sapphire. |
| 3.1-2 | The total area of the bulk solar-wind collectors shall be > 0.6 m2. | Sample size required to achieve precision goals, including allowance for some duplication of measurements and to address the requirement for a reservoir of solar matter for the 21st century. | The payload design goal is to maximize collector area. |
| 3.1-3 | The area of each of the 3 special-regime collectors shall be > 0.3 m2. | As in 3.1-2. | As in 3.1-2. |
| 3.1-4 | Temperatures of collector array materials used for solar wind analysis shall not exceed 200° C for Si and not exceed 250_ C for other such materials at all times during and following solar wind exposure. | Necessary to minimize diffusion of sample deeper into or out of the collectors. | Higher temperatures are acceptable prior to exposure. |
| 3.1-5 | The collector array of each sample collector shall be uniquely identifiable. | To enable recognition of solar wind regime of each sample even if the collector arrays are smashed and shuffled during recovery. | Most likely achievable with differences in array material thickness. |
| 3.1-6 | Collector materials for measurement of solar wind radioactive nuclei shall be exposed to Sun in lid of SRC. | There are no contamination issues, so these materials can be outside the canister. | Area and composition of these materials shall be adjusted to meet flight system requirements. |
| 3.1-7 | At least TBD% of array materials shall remain in the array frames at the time of canister disassembly. At least 1/3 of the array materials shall be unfractured. | Array materials from individual arrays can be recognized (see 3.1.5); however broken pieces recovered from the bottom of the canister have a high risk of surface abrasion and loss of solar wind signal. As long as the wafer remains in the array frame, some fracturing is acceptable. | A mission goal is to return unbroken collector materials. Intact but fractured wafers are scientifically useful, but these are a significant complication to canister disassembly, thus imparting risk to the Phase E science schedule. |
| No. | Requirement | Rationale | Comments |
| 3.2-1 | The average concentration factor for N and O shall be >20. | Requirement based on measurements of purity of possible target materials and amounts of solar wind O required to meet analytical precision. | |
| 3.2-2 | The area of the concentrator target implanted with solar wind shall be >15 cm2. | Requirement based on estimates of projected technology for measurement of O isotopes and strawman sample allocations. | |
| 3.2-3 | The concentrator must not introduce errors in the ratio of 17O:16O > 0.1% | Required to meet precision requirements for the highest priority science objective. | General requirement is firm, but it can be accomplished by a combination of instrument performance analysis and calibration. |
| 3.2-4 | The concentrator target temperature shall not exceed 250°C. | Required to prevent diffusion of implanted atoms. | |
| 3.2-5 | The ions shall be accelerated through a potential of at least 8 kV before impacting the concentrator target. | To increase penetration into target material to help separate sample from surface contamination; improves ion optics. | Near isotropic angular distribution of ions on target makes depth profiles broader and more shallow. High voltages in the 10-15 kV range are desirable. |
| 3.2-6 | TBD of the solar wind proton fluence shall be prevented from reaching the concentrator target. | Required to decrease the chance of blistering the target material. | Goal is 90% rejection. |
| No. | Requirement | Rationale | Comments |
| 3.3-1 | Collector materials must be sufficiently pure that accuracy/precision requirements in Table 2 can be met. | Provide adequate signal-to-background. | Typically, this will require bulk concentrations of contami-nants be less than 1% of the average concentration of the solar wind in outer 100 nanometers. |
| 3.3-2 | At the time of analysis, surface contamination by C, N, O must be < 1015 atoms/cm2 under ultra-high vacuum (<10-8 torr.) conditions at 200° C. | Surface contamination at these levels can be resolved from implanted solar wind. | Handling and cleaning procedures are covered in the Genesis Contamination Control Plan. |
| 3.3-3 | Other than C, N, O, the number of atoms/cm2 of each surface contaminant at the time of analysis shall not exceed the estimated solar wind fluence of the species as given in Table 3. | Surface contamination at these levels can be resolved from the implanted solar wind. | |
| 3.3-4 | The gas phase in the science canister shall not result in contamina-tion levels greater than set in 3.3-2 and 3.3-3. | The environment in the reentry capsule during reentry will be relatively dirty. Protection of collector surfaces from this environment is required. | This requirement is implicit in 3.3-2 and 3.3-3, but is listed explicitly to highlight specific design efforts. Baseline mission design incorporates a N2 purge before launch and a filter to clean the air during pressurization accompanying reentry. |
| No. | Requirement | Rationale | Comments |
| 3.4-0 | The ion and electron monitor shall determine which type of solar wind is present: interstream, coronal hole, or coronal mass ejection. | Enables meeting several of the mission objectives. See Requirement 1-2. | An on-board algorithm uses the monitor data to determine solar wind regime. |
| 3.4-1 | Once solar wind regime is identified, the appropriate solar wind array shall be deployed. | See Requirement 1-2 | |
| 3.4-1.1 | Upon decision by the on-board algorithms, exchange of collector arrays shall be completed within 2 data cycles (See 3.5-4). | Required to prevent excessive mixing of wind from different regimes. | Mechanism actuation and array deployment times need not be rapid. |
| 3.4-1.2 | It shall be possible to change which specific solar wind collector is exposed at least 400 times during the 2-year exposure. | Based on applying preliminary algorithms to ISEE-3 data and multiplying by 2 to account for different solar cycle phase. | This requirement can implemented by extensive ground testing to far more than 400 cycles. |
| 3.4-2 | The data from the monitors shall be used to control the voltages in the concentrator. | The concentrator voltages must be tuned to the so-lar wind speed to avoid mass fractionation, to re-ject protons (but not heavy ions) from the target, and to maintain concentration effi-ciency. | Nominally based on the ion monitor data; electron monitor data can serve as backup. |
| 3.4-2.1 | Upon decision by the on-board algorithms, the time lag to change concentrator voltages shall not to exceed 2 data cycles (See 3.5-4) from the time the data are acquired. | The time requirement is to permit the S/C computer to complete other tasks, if necessary. | Need to control voltages is firm; time lag is negotiable if necessary. |
| No. | Requirement | Rationale | Comments |
| 3.5-1 | There shall be no line of sight of front collector surfaces to any part of the spacecraft or sample reentry capsule. (Interior canister surfaces are excluded from this requirement.) | Avoid contamination of collectors by outgassed spacecraft and reentry capsule volatiles or by micrometeorite ejecta from flight system components. | Some line-of-sight of collector front surfaces to interior portions of canister is unavoidable, but acceptable because canister interior materials are clean. Solid angles for this exposure will be minimized in payload design. Some line of sight exposure of the back sides of collector arrays to the SRC is also unavoidable, but mission design will mitigate the effects of such second order contamination. |
| 3.5-2 | The spacecraft shall provide a clear field of view for the ion monitor consisting of a fan ³20° long by ³10° wide, with one edge aligned with the sunward spin axis to an accuracy of (+2 -0)° (See Figure 1). | Include all likely directions of incidence of solar-wind ions during each spin period. | Field of view may extend up to 2 deg. beyond the spin axis, but must include, or be adjacent to, the spin axis. |
| 3.5-3 | The spacecraft shall provide a clear field of view for the electron monitor consisting of a fan extending from ²10° to ³170° from the spin axis by ³30° wide. (See Fig. 1). | Map the 3-D distribution of solar-wind electrons during each spin period. | The electron monitor field of view will exclude the solar direction to minimize interference from photoelectrons. |
| 3.5-4 | The 3-D ion and elec-tron distributions shall be measured within a 2.5±1.5 min. period. | A complete 3-D measurement over this amount of time limits errors from time aliasing of the data. | |
| 3.5-5 | The spacecraft shall provide a clear field of view of the concentrator consisting of a cone with half-angle ³15° as shown in Figure 2. | Required to collect > 95% of the ions over the expected variations of solar wind directions and spin axis pointing. | |
| 3.5-6 | The science team requires 60kb per data cycle with ²2.5 minute duration. For data cycles with >2.5 minute duration, the data volume shall increase to support a constant 400b/s on-board data generation rate. | Required to assess proper functioning of the monitors, velocity and regime determination processes. | These data volumes and rates do not include any overhead for on-board handling or for delivery to the science team. The minimum of 400bps is constantly generated on-board the spacecraft during data cycles of ³2.5 minutes, and consists of the monitors’ science and housekeeping data, and a record of on-board determinations of solar wind speed and regime. For data cycles of <2.5 minutes, the data rate increases to maintain 60kb per cycle. 400bps and 60kb are preliminary estimates. Data compression algorithms, if necessary, are negotiable. |
| No. | Requirement | Rationale | Comments |
| 3.6-1 | During exposure, the perpendicular to the collector arrays shall point within 10 deg. of the solar-wind flow direction, which is assumed to be, on average, 4.5° forward (in the sense of the spacecraft motion about the Sun) of the center of the Sun. | Near-normal incidence required for deepest penetration and greatest retention of solar wind ions. | Less stringent than require-ment 3.6-3. Occasional wide-but-short ex-cursions permissible. |
| 3.6-3 | During exposure, the boresight of the concentrator shall be pointed 4.5 ± 2.0° forward of the center of the Sun. | This offset corrects for the average aberration of the arrival direction of the solar wind and keeps the concentrator close to its optimum performance (normal incidence). | The angular range includes contributions from any misalignment of the concentrator and/or spin axes, any wobble of the spin axis, and drifts between maneuvers to re-orient the spin axis. Occasional wide-but-short excursions permissible |
| 3.6-4 | The azimuthal look directions of the ion and electron monitors shall be available on-board to an angular accuracy of 2 ± 1 deg. | Necessary for calculating view directions from the ion and electron monitor data for use in computing solar wind regime. | A "sun pulse" would be adequate. |
| 3.6-5 | Wobble or nutation of the spin axis shall be no greater than 0.5 degrees over a monitor data collection cycle (nominally 2.5 minutes; see 3.5-4). | Spin axis variations greater than this will appear to increase the plasma temperature and interfere with the calculation of the solar wind regime. | Occasional exceptions permissible if data are so flagged. |
| 3.6-6 | Data on the spin axis orientation shall be included in the telemetry stream with time resolution no coarser than the monitor data cycle (nominally 2.5 minutes; see 3.5-4 ) and angular accuracy of 1°. | Required for interpretation of 3D ion and electron dis-tributions and checking the regime algorithms. | |
| 3.6-7 | The spacecraft spin period shall be equal to or less than the monitor data cycle (nominally 2.5 minutes; see 3.5-4 ). | Determination of solar wind parameters requires measurements covering all spin phases. |
Figure 1. Fields of view of the ion and electron monitors
(Note: although, in this projection, the canister lid appears to block the field of view of the electron monitor, this is not the case in three dimensions.)
Figure 2. Diagram of the field of view of the concentrator
| No. | Requirement | Rationale | Comments |
| 4-1 | During sample exposure, the full resolution 3-D distributions of ions and electrons shall be telemetered to Earth at least once a week. | Required to (1) check the performance of the solar-wind regime algorithm, (2) calculate any mass fractionation correction for the concentrator, and (3) document the proper-ties of the solar wind dur-ing the sample collection. | Transmission frequency may be re-duced toward end of mission. |
| 4-2 | It shall be possible to change the on-board algorithms for determining the solar wind regime or for controlling the concentrator voltages by means of an uplink message from Earth. | The pre-stored algorithms might not work as well as predicted from old solar wind data. If the ion monitor fails, the electron monitor can be used to set the concentrator voltages. | |
| 4-3 | Monitor data shall be acquired and analyzed for as long as possible before the start of sample exposure. | Required to check out performance of the monitors and the regime algorithms. | Suggested scenario: (1) Remove monitor covers approximately an hour after the final TCM (nominally occurs two weeks after launch). (2) Begin monitor turn-on procedures 2 to 3 days later. |
5. Sample and Data Analysis and Archiving
| No. | Requirement | Rationale | Comments |
| 5-1 | Develop analysis instru-ments and techniques with sufficient sensitivity and accuracy to carry out the prioritized measurement objectives listed in Tables 1 to the accuracy/precision given in Table 2. | Necessary to success of mission objectives. | A firm requirement. A number of candidate techniques are described in the Genesis discovery 5 Proposals and in the Genesis Project Implementation Plan. |
| 5-2 | As part of disassembly protocol, documentation of locations of individual wafer fragments in science canister shall be maintained. | Required for identification of solar wind regime and of any localized contamination from meteorites or other sources. | Prior to launch all wafers of a given material in a given array are equivalent, and less documen-tation is re-quired. |
| 5-3 | Returned collector materials shall be curated while maintaining cleanliness requirements from 3.3-2 and 3.3-3. | Analytical techniques are expected to improve with time, allowing increasingly accurate analyses. Implements requirement to provide reservoir of solar material for 21st century. | |
| 5-4 | Facilities shall be developed for distributing samples to investigators while maintaining cleanliness requirements from 3.3-2 and 3.3-3. | Necessary to meet science objectives. | |
| 5-5 | A database of investigator allocations shall be maintained. | Necessary in case of unanticipated results. This requirement supports possibility of reallocation of unused materials from the first round of analysis. |
Backshell: The trailing surface of the SRC during reentry. This needs to be distinguished from the front nose cone surface of the SRC because the backshell has a different ablator material.
Collector materials: This is a general phrase. Collector array materials or array materials refers to materials on the deployable arrays. The materials in the concentrator are referred to as target materials.
Cover: The canister has a cover. The SRC has a lid.
Flux: Number of particles per unit area per unit time. The solar wind proton flux is 3 x 108/cm2-sec.
Fluence: Flux times time, i.e. particles/cm2.
Lid: The SRC has a lid. The canister has a cover.
SRC: refers to Sample Return Capsule.
Target materials: This phrase is used for the materials used to collect the concentrated solar wind in the concentrator.