Chapter 5
Q. 5.12
Starting with the state vector determined in Example 5.11, use Algorithm 5.6 to improve the vector to five significant figures.
Step-by-Step
Verified Solution
Step 1:
r_2=\left\| r _2\right\|=\sqrt{5659.1^2+6533.8^2+3270.1^2}=9241.8 km
v_2=\left\| v _2\right\|=\sqrt{(-3.8800)^2+5.1156+(-2.2397)^2}=6.7999 km / s
Step 2:
\alpha=\frac{2}{r_2}-\frac{v_2^2}{\mu}=\frac{2}{9241.8}-\frac{6.7999^2}{398,600}=1.0154\left(10^{-4}\right) km ^{-1}
Step 3:
\left.v_r\right)_2=\frac{ v _2 \cdot r _2}{r_2}=\frac{(-3.8800) \cdot 5659.1+5.1156 \cdot 6533.8+(-2.2397) \cdot 3270.1}{9241.8}=0.44829 km / s
Step 4:
The universal Kepler equation at times t_1 and t_3, respectively, becomes
\sqrt{398,600} \tau_1=\frac{9241.8 .0 \cdot 44829}{\sqrt{398,600}} \chi_1^2 C\left(1.0040 \times 10^{-4} \chi_1^2\right)
+\left(1-1.0040 \times 10^{-4} \cdot 9241.8\right) \chi_1^3 S\left(1.0040 \times 10^{-4} \chi_1^2\right)+9241.8 \chi_1
\sqrt{398,600} \tau_3=\frac{9241.8 \cdot 0.44829}{\sqrt{398,600}} \chi_3^2 C\left(1.0040 \times 10^{-4} \chi_3^2\right)
+\left(1-1.0040 \times 10^{-4} \cdot 9241.8\right) \chi_3^3 S\left(1.0040 \times 10^{-4} \chi_3^2\right)+9241.8 \chi_3
or
631.35 \tau_1=6.5622 \chi_1^2 C\left(1.0040 \times 10^{-4} \chi_1^2\right)+0.072085 \chi_1^3 S\left(1.0040 \times 10^{-4} \chi_1^2+9241.8 \chi_1\right)
631.35 \tau_3=6.5622 \chi_3^2 C\left(1.0040 \times 10^{-4} \chi_3^2\right)+0.072085 \chi_1^3 S\left(1.0040 \times 10^{-4} \chi_3^2+9241.8 \chi_3\right)
Applying Algorithm 3.3 to each of these equations yields
\chi_1=-8.0908 \sqrt{ km }
\chi_3=8.1375 \sqrt{ km }
Step 5:
f_1=1-\frac{\chi_1^2}{r_2} C\left(\alpha \chi_1^2\right)=1-\frac{(-8.0908)^2}{9241.8} \cdot \overbrace{C\left(1.0040 \times 10^{-4}[-8.0908]^2\right)}^{0.49973}=0.99646
g_1=\tau_1-\frac{1}{\sqrt{\mu}} \chi_1^3 S\left(\alpha \chi_1^2\right)
=-118.1-\frac{1}{\sqrt{398,600}}(-8.0908)^3 \cdot \overbrace{S\left(1.0040 \times 10^{-4}[-8.0908]^2\right)}^{0.16661}=-117.96 s
and
f_3=1-\frac{\chi_3^2}{r_2} C\left(\alpha \chi_3^2\right)=1-\frac{8.1375^2}{9241.8} \cdot \overbrace{C\left(1.0040 \times 10^{-4} \cdot 8.1375^2\right)}^{0.49972}=0.99642
g_3=\tau_3-\frac{1}{\sqrt{\mu}} \chi_3^3 S\left(\alpha \chi_3^2\right)
=-118.1-\frac{1}{\sqrt{398,600}} 8.1375^3 \cdot \overbrace{S\left(1.0040 \times 10^{-4} \cdot 8.1375^2\right)}^{0.16661}=119.33
It turns out that the procedure converges more rapidly if the Lagrange coefficients are set equal to the average of those computed for the current step and those computed for the previous step. Thus, we set
f_1=\frac{0.99648+0.99646}{2}=0.99647
g_1=\frac{-117.97+(-117.96)}{2}=-117.96 s
f_3=\frac{0.99642+0.99641}{2}=0.99641
g_3=\frac{119.33+119.33}{2}=119.34 s
Step 6:
c_1=\frac{119.33}{(0.99647)(119.33)-(0.99641)(-117.96)}=0.50467
c_3=\frac{-117.96}{(0.99647)(119.33)-(0.99641)(-117.96)}=0.49890
Step 7:
\rho_1=\frac{1}{-0.0015198}\left(-782.15+\frac{1}{0.50467} 787.72-\frac{0.49890}{0.50467} 787.31\right)=3650.6 km
\rho_2=\frac{1}{-0.0015198}(-0.50467 \cdot 1646.5+1651.5-0.49890 \cdot 1656.6)=3877.2 km
\rho_3=\frac{1}{-0.0015198}\left(-\frac{0.50467}{0.49890} 887.10+\frac{1}{0.49890} 889.60-892.13\right)=4186.2 km
Step 8:
r _1=(3489.8 \hat{ I }+3430.2 \hat{ J }+4078.5 \hat{ K })+3650.6(0.71643 \hat{ I }+0.68074 \hat{ J } -0.15270 \hat{ K })
=6105.2 \hat{ I }+5915.3 \hat{ J }+3521.1 \hat{ K } ( km )
r _2=(3460.1 \hat{ I }+3460.1 \hat{ J }+4078.5 \hat{ K })+3877.2(0.56897 \hat{ I }+0.79531 \hat{ J }-0.20917 \hat{ K })
=5666.6 \hat{ I }+6543.7 \hat{ J }+3267.5 \hat{ K } ( km )
r _3=(3429.9 \hat{ I }+3490.1 \hat{ J }+4078.5 \hat{ K })+4186.2(0.41841 \hat{ I }+0.87007 \hat{ J } -0.26059 \hat{ K })
=5181.4 \hat{ I }+7132.4 \hat{ J } +2987.6 \hat{ K } ( km )
Step 9:
v _2=\frac{1}{0.99647 \cdot 119.33-0.99641(-117.96)}
\times[-0.99641(6105.2 \hat{ I }+5915.3 \hat{ J }+3521.1 \hat{ K })+0.99647(5181.4 \hat{ I }+7132.4 \hat{ J }+2987.6 \hat{ K })]
=-3.8856 \hat{ I }+5.1214 \hat{ J }-2.2434 \hat{ K } ( km / s )
This completes the first iteration.
The updated position r_2 and velocity v_2 are used to repeat the procedure beginning at Step 1. The results of the first and subsequent iterations are shown in Table 5.2. Convergence to five significant figures in the slant ranges \rho_1, \rho_2, and \rho_3occurs in four steps, at which point the state vector is
r _2=5662.1 \hat{ I }+6538.0 \hat{ J }+3269.0 \hat{ K } ( km )
v _2=-3.8856 \hat{ I }+5.1214 \hat{ J }-2.2433 \hat{ K } ( km / s )
Using r_2 and v_2 in Algorithm 4.2, we find that the orbital elements are
a = 10,000 km (h = 62,818km²/s)
e = 0.1000
i = 30°
Ω = 270°
ω = 90°
θ = 45.01°
Table 5.2 Key results at each step of the iterative procedure
Step | \chi_1 | \chi_2 | f_1 | g_1 | f_3 | g_3 | \rho_1 | \rho_2 |
\rho_3
|
1 | -8.0908 | 8.1375 | 0.99647 | -117.97 | 0.99641 | 119.33 | 3650.6 | 3877.2 | 4186.2 |
2 | -8.0818 | 8.1282 | 0.99647 | -117.96 | 0.996 42 | 119.33 | 3643.8 | 3869.9 | 4178.3 |
3 | -8.0871 | 8.1337 | 0.99647 | -117.96 | 0.996 42 | 119.33 | 3644.0 | 3870.1 | 4178.6 |
4 | -8.0869 | 8.1336 | 0.99647 | -117.96 | 0.996 42 | 119.33 | 3644.0 | 3870.1 | 4178.6 |