  Let $\gamma:[0,1]\rightarrow \mathbb{S}^{2}$ be a non-degenerate curve in
$\mathbb{R}^3$, that is to say,
$\det\big(\gamma(\theta),\gamma'(\theta),\gamma''(\theta)\big)\neq 0$. For each
$\theta\in[0,1]$, let $l_\theta=\{t\gamma(\theta):t\in\mathbb{R}\}$ and
$\rho_\theta:\mathbb{R}^3\rightarrow l_\theta$ be the orthogonal projections.
  We prove an exceptional set estimate. For any Borel set
$A\subset\mathbb{R}^3$ and $0\le s\le 1$, define $E_s(A):=\{\theta\in[0,1]:
\text{dim}(\rho_\theta(A))<s\}$. We have $\text{dim}(E_s(A))\le
1+\frac{s-\text{dim}(A)}{2}$.
