135 lines
5.0 KiB
Rust
135 lines
5.0 KiB
Rust
//! The impulsive maneuver.
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//!
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//! 脉冲机动。
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use crate::error::{ManeuverError, ManeuverErrorKind};
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use apsis_math::Vec3;
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/// An instantaneous change in velocity.
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///
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/// An impulse is a velocity change applied in zero time, so it changes the
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/// velocity of a state but not its position. That is the model for a burn
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/// short compared with the orbital period, and it is how a delta-v budget is
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/// written.
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///
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/// The change is stored as a vector in the same frame as the state it will
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/// be applied to, so the caller is responsible for expressing it in that
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/// frame. The magnitude is the delta-v, the quantity a propellant budget is
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/// measured in.
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///
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/// 瞬时速度变化。
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///
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/// 冲量是在零时间内施加的速度变化，故只改变状态的速度而不改变其位置。这是相对
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/// 轨道周期很短的点火的模型，也是编写 delta-v 预算所用的模型。
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///
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/// 该变化以矢量形式存储在与待施加状态相同的坐标系中，因此调用方负责把它表达
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/// 在该系中。其模即 delta-v，推进剂预算以此计量。
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#[derive(Debug, Clone, Copy, PartialEq)]
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pub struct Impulse {
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delta_v: Vec3,
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}
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impl Impulse {
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/// Creates an impulse from a velocity change vector, in kilometers per
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/// second.
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///
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/// Returns an error when a component is not finite or when the vector is
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/// zero, because a zero change is not a maneuver and is almost always a
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/// mistake in a plan.
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///
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/// 由速度变化矢量创建冲量，单位为千米每秒。
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///
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/// 当某个分量非有限或矢量为零时返回错误，因为零变化不是机动，且几乎总是
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/// 计划中的笔误。
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pub fn new(delta_v: Vec3) -> Result<Self, ManeuverError> {
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if !delta_v.is_finite() {
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return Err(ManeuverError::new(ManeuverErrorKind::NotFinite)
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.with_detail("the velocity change is not finite"));
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}
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if delta_v.norm() == 0.0 {
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return Err(ManeuverError::new(ManeuverErrorKind::InvalidState)
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.with_detail("the velocity change is zero"));
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}
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Ok(Self { delta_v })
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}
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/// Creates an impulse of a given magnitude along a direction.
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///
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/// The direction is normalized, so the magnitude is the delta-v whatever
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/// the length of the direction vector. Returns an error when the
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/// magnitude is not positive and finite or when the direction is zero or
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/// not finite.
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///
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/// 沿给定方向创建指定大小的冲量。
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///
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/// 方向被归一化，故无论方向矢量多长，其大小即 delta-v。当大小非正或非有限，
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/// 或方向为零或非有限时返回错误。
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pub fn along(direction: Vec3, magnitude: f64) -> Result<Self, ManeuverError> {
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if !magnitude.is_finite() || magnitude <= 0.0 {
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return Err(
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ManeuverError::new(ManeuverErrorKind::NonPositiveAcceleration)
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.with_detail(format!("magnitude {magnitude}")),
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);
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}
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let unit = direction.normalize().ok_or_else(|| {
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ManeuverError::new(ManeuverErrorKind::InvalidState)
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.with_detail("the direction is zero or not finite")
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})?;
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Self::new(unit * magnitude)
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}
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/// Returns the velocity change vector, in kilometers per second.
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///
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/// 返回速度变化矢量，单位为千米每秒。
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pub const fn delta_v(self) -> Vec3 {
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self.delta_v
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}
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/// Returns the magnitude of the change, in kilometers per second.
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///
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/// This is the delta-v the burn costs.
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///
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/// 返回该变化的大小，单位为千米每秒。
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///
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/// 这就是该次点火所需的 delta-v。
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pub fn magnitude(self) -> f64 {
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self.delta_v.norm()
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}
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/// Returns a copy of the change scaled by a factor.
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///
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/// A factor of zero produces a zero impulse, which [`Impulse::new`]
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/// rejects, so this returns an error for it rather than a value that
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/// cannot be built.
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///
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/// 返回该变化按某因子缩放后的副本。
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///
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/// 因子为零会得到零冲量，而 [`Impulse::new`] 拒绝这种情况，故本函数对该
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/// 因子返回错误，而不是给出一个无法构造的值。
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pub fn scaled(self, factor: f64) -> Result<Self, ManeuverError> {
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Self::new(self.delta_v * factor)
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}
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/// Returns a copy of the change reversed, which undoes the burn.
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///
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/// 返回取反后的变化副本，即撤销该次点火。
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pub fn reversed(self) -> Self {
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Self {
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delta_v: -self.delta_v,
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}
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}
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/// Applies the impulse to a velocity, returning the new velocity.
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///
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/// 把该冲量作用于一个速度，返回新的速度。
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pub fn apply_to_velocity(self, velocity: Vec3) -> Vec3 {
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velocity + self.delta_v
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}
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}
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impl core::fmt::Display for Impulse {
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fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
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write!(f, "impulse of {:.6} km/s", self.magnitude())
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}
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}
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